Split separate module tests

[LukeSavefrogs]

Each module should have its own CI test, to spot immediately what is failing and why.

For example, the polyfills.json module would have:

• .github/workflows/tests-json-cpython.yml:

  python ./scripts/run_tests.py -s src/polyfills/json -p "*.py" -v

• .github/workflows/tests-json-jython.yml:

  jython ./scripts/run_tests.py -s src/polyfills/json -p "*.py" -v

In the meantime, the polyfills.pathlib module would have:

• .github/workflows/tests-pathlib-cpython.yml:

  python ./scripts/run_tests.py -s src/polyfills/pathlib -p "*.py" -v

• .github/workflows/tests-pathlib-jython.yml:

  jython ./scripts/run_tests.py -s src/polyfills/pathlib -p "*.py" -v

[LukeSavefrogs]

It seems that sub-folder organization is still not possible, so for now I divided the tests by OS