M0: validate the committed parity manifest in xtask tests (#1214)

Parse the committed parity manifest in the existing xtask unit-test suite
so duplicate TOML keys fail cargo test --workspace.

Co-authored-by: srt8hellcat2-ui <225485253+srt8hellcat2-ui@users.noreply.github.com>

xtask/src/parity.rs

@@ -251,6 +251,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn committed_manifest_is_well_formed() {
+        let path = root().join("parity/acrobat-features.toml");
+        let text = std::fs::read_to_string(&path).expect("read the committed parity manifest");
+        let _: File = toml::from_str(&text).expect("the committed parity manifest must be valid TOML");
+    }
+
     #[test]
     fn registry_ids_are_extracted_from_source() {
         let src =