Serialize coverage tests

Author: ozankasikci

.github/workflows/coverage.yml

@@ -29,7 +29,7 @@ jobs:
 
       - name: Generate coverage report
         run: |
-          cargo llvm-cov --workspace --locked --lcov --output-path lcov.info
+          cargo llvm-cov --workspace --locked --lcov --output-path lcov.info -- --test-threads=1
         env:
           CARGO_INCREMENTAL: "0"