fix(test): Serialize unit tests for MinGW dlltool

It appears to use temporary object files which collide even
when the output file paths are different.

Author: ravenexp

.github/workflows/rust.yml

@@ -26,7 +26,7 @@ jobs:
     - name: Build
       run: cargo build --verbose
     - name: Run tests
-      run: cargo test --verbose
+      run: cargo test --verbose -- --test-threads=1
   zigbuild:
     name: Test zig dlltool
     runs-on: ubuntu-latest