Update build-test-package.yml

Action failed previously due to the lack of pytest packages

.github/workflows/build-test-package.yml

@@ -38,6 +38,10 @@ jobs:
           # Confirm installation
           pip show mloptimizer
 
+      - name: Install pytest not included in mloptimizer
+        run: |
+          python -m pip install pytest pytest-mock pytest-cov
+
       # Run tests to ensure package works as expected without source code
       - name: Run package tests
         run: |