The test checked that Japanese text falls back to an installed Japanese
family, but left the process-global CJK locale at the host's: on a zh-CN
host with a Chinese face installed, han_order puts the Chinese families
first for the shared ideographs and the Japanese-family assertion fails.
Set ja-JP under the TEST_CJK_LOCALE lock and clear the request when the
test ends, as the zh-CN test beside it does.
Tests: effectcraft-text 75 lib + 3 integration passed; cargo fmt --all -- --check passed.
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