try this one

Author: DifferentialOrange

.github/workflows/testing.yml

@@ -318,7 +318,7 @@ jobs:
           python-version: ${{ matrix.python }}
 
       - name: Install the package with pip
-        run: pip install git+$env:GITHUB_SERVER_URL/$env:GITHUB_REPOSITORY@$env:GITHUB_REF_NAME
+        run: python -m pip install git+$env:GITHUB_SERVER_URL/$env:GITHUB_REPOSITORY@$env:GITHUB_REF_NAME
 
       - run: pip --version