Update python-app.yml

Fixing to indicate that unittest (not pytest) is used.

.github/workflows/python-app.yml

@@ -25,6 +25,6 @@ jobs:
         python -m pip install --upgrade pip
         pip install numpy
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
-    - name: Test with pytest
+    - name: Test with unittest
       run: |
         python3 -m unittest tests/test_egrssmatrix.py