don't test in parallel

We don't need parallel testing. There are not many tests, and it makes
the output harder to read.

Author: haarg

.github/workflows/build-and-test.yml

@@ -83,7 +83,7 @@ jobs:
           --show-build-log-on-failure
       - name: Run Tests
         if: success()
-        run: prove -lrv --jobs 2 t
+        run: prove -lrv t
   test_macos:
     runs-on: ${{ matrix.os }}
     strategy: