Enable parallel testing

Author: AlexNachbaur

.github/workflows/tests.yaml

@@ -208,7 +208,7 @@ jobs:
     - name: Test
       run: |
         set -o pipefail
-        swift test $SWIFT_ARGUMENTS --verbose 2>&1 | tee -a .build/ci-logs/${LOG_NAME}-test.log | xcbeautify $XCBEAUTIFY_ARGS
+        swift test $SWIFT_ARGUMENTS --parallel --verbose 2>&1 | tee -a .build/ci-logs/${LOG_NAME}-test.log | xcbeautify $XCBEAUTIFY_ARGS
     - name: Upload Logs
       if: failure()
       uses: actions/upload-artifact@v4