Clean up/fix ccpp_prebuild CI tests (#533)

Fixes the issues mentioned in #532 so that CI tests should now all run successfully:

 - Correctly run `test_metadata_parser.py` and `test_mkstatic.py` with `pytest`
 - Remove old testing files `python.yaml` and `pytest.ini`

In addition, I implemented multi-version python testing (all active Python versions: 3.8 through 3.12) rather than just a single version.

.github/workflows/prebuild.yaml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.10"]
+        python-version: ["3.8","3.9","3.10","3.11","3.12"]
 
     steps:
     - uses: actions/checkout@v4
@@ -35,8 +35,7 @@ jobs:
       run: |
         export PYTHONPATH=$(pwd)/scripts:$(pwd)/scripts/parse_tools
         cd test_prebuild
-        python3 test_metadata_parser.py
-        python3 test_mkstatic.py
+        pytest
     - name: ccpp-prebuild blocked data tests
       run: |
         cd test_prebuild/test_blocked_data