[MNT] added pytest run command for github CI (#686)

## Change(s)
in the `.github\workflows\pytest-tests.yml` file for `Run Unit Test via
Pytest` does not contain any workflow to run the actual `pytests`. the
jobs currently do:
- Setup Python virtual environment
- Install dependencies
- pre-commit check

added the job to run pytest at the end:
```yaml
    - name: Run pytest
      run: |
        source venv/bin/activate
        pytest src/tests
```

this should enable running the ctual pytests on github CI.

Solves #684

Author: rohansen856

.github/workflows/pytest-tests.yml

@@ -40,3 +40,8 @@ jobs:
       run: |
         source venv/bin/activate
         pre-commit run --all
+
+    - name: Run pytest
+      run: |
+        source venv/bin/activate
+        pytest src/tests