ci: use sequential execution for strict mode tests

Avoid flaky parallel race conditions in CI environment

Author: Chemaclass

.github/workflows/tests.yml

@@ -120,4 +120,4 @@ jobs:
 
       - name: Run Tests with strict mode
         run: |
-          ./bashunit --parallel --simple --strict tests/
+          ./bashunit --no-parallel --simple --strict tests/