CI: run the Linux without-heif and craft-fonts builds in parallel

They ran after the main tests in the Linux test job and added ~10 min to its critical path (and
were why that job ran out of disk). Now a two-leg job restores the test job's cache read-only
(shared-key: test) and saves nothing, so the cache budget (#2688) doesn't grow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -136,33 +136,6 @@ jobs:
       - name: Doctests
         run: cargo test --workspace --locked --features heif --doc
 
-      # The same codecs without the optional decoder: HEIC must stay a clear "not in this build"
-      # error for distributors who leave it out.
-      - name: Test without heif
-        if: runner.os == 'Linux'
-        run: cargo test -p photocraft-heif -p photocraft-codecs -p photocraft-io --locked
-
-      # The same tests built with the optional craft-fonts input (crates/text/build.rs), so the
-      # Japanese font tests that skip without it run here. Linux only. Keep the exact `--workspace
-      # --features heif --lib --bins --tests` of the Test step: any other package, target or
-      # feature selection resolves a different feature set, recompiles the whole dependency graph
-      # into the same target dir and runs the runner out of disk (as `-p photocraft-text -p
-      # photocraft-ui-egui` did after #800).
-      - name: Check out craft-fonts
-        if: runner.os == 'Linux'
-        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
-        with:
-          repository: storytold/craft-fonts
-          ref: abb83316d96aa59c1cf64784289e378fe9fa5695
-          path: craft-fonts
-
-      - name: Test with craft-fonts
-        if: runner.os == 'Linux'
-        env:
-          CRAFT_FONTS_DIR: ${{ github.workspace }}/craft-fonts
-          CRAFT_FONTS_REQUIRED: "1"
-        run: cargo nextest run --workspace --locked --features heif --lib --bins --tests --no-fail-fast
-
       - name: Clippy
         run: cargo clippy --workspace --all-targets --locked --features heif -- -D warnings
 
@@ -175,6 +148,65 @@ jobs:
         if: runner.os == 'Linux'
         run: cargo xtask scorecard --check
 
+  # The two other builds of the Linux tests, in parallel with the test job instead of after it (they
+  # added ~10 min to its critical path). Each restores the test job's cache (`shared-key: test` is
+  # that job's key) and saves none: the dependencies are the same, and the 10 GB cache budget is
+  # tight (#2688).
+  test-variants:
+    name: test (${{ matrix.variant }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        variant: [without heif, with craft-fonts]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Linux system dependencies (egui/winit/rfd)
+        run: |
+          nohup sudo rm -rf /usr/local/lib/android /usr/share/dotnet /opt/ghc /usr/local/.ghcup \
+            /opt/hostedtoolcache/CodeQL </dev/null >/dev/null 2>&1 &
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            libxkbcommon-dev libwayland-dev libx11-dev libxrandr-dev libxi-dev \
+            libgl1-mesa-dev libgtk-3-dev
+
+      - uses: dtolnay/rust-toolchain@stable
+
+      - uses: Swatinem/rust-cache@v2
+        with:
+          shared-key: test
+          save-if: false
+
+      - uses: taiki-e/install-action@9983c65e42da123ff25d1f78505eb6de315aa172 # v2.87.20
+        if: matrix.variant == 'with craft-fonts'
+        with:
+          tool: cargo-nextest@0.9.146
+
+      # The same codecs without the optional decoder: HEIC must stay a clear "not in this build"
+      # error for distributors who leave it out.
+      - name: Test without heif
+        if: matrix.variant == 'without heif'
+        run: cargo test -p photocraft-heif -p photocraft-codecs -p photocraft-io --locked
+
+      # The tests built with the optional craft-fonts input (crates/text/build.rs), so the Japanese
+      # font tests that skip without it run. Keep the test job's exact `--workspace --features heif
+      # --lib --bins --tests`, so the restored dependencies match and only the workspace rebuilds.
+      - name: Check out craft-fonts
+        if: matrix.variant == 'with craft-fonts'
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4
+        with:
+          repository: storytold/craft-fonts
+          ref: abb83316d96aa59c1cf64784289e378fe9fa5695
+          path: craft-fonts
+
+      - name: Test with craft-fonts
+        if: matrix.variant == 'with craft-fonts'
+        env:
+          CRAFT_FONTS_DIR: ${{ github.workspace }}/craft-fonts
+          CRAFT_FONTS_REQUIRED: "1"
+        run: cargo nextest run --workspace --locked --features heif --lib --bins --tests --no-fail-fast
+
   corpus:
     # Real-file corpus tests (cargo feature `corpus`), on every PR and on main. The corpora are
     # pinned in xtask/src/corpus_pins.rs and sha256-verified (xtask/*.sha256) after both a cache