Fix deprecation warning of CI (#330)

Fix deprecation warning of CI by replacing output variables with pip cache

Author: sebheger

.github/workflows/github-ci.yml

@@ -63,24 +63,14 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
         architecture: x64
+        cache: 'pip'
 
     - name: Check python version
       run: python -c "import sys; import platform; print('Python %s implementation %s on %s' % (sys.version, platform.python_implementation(), sys.platform))"
 
     - name: Upgrade pip
       run: python -m pip install --upgrade pip
 
-    - name: Get pip cache dir
-      id: pip-cache
-      run: |
-        echo "::set-output name=dir::$(pip cache dir)"
-
-    - name: pip cache
-      uses: actions/cache@v3
-      with:
-        path: ${{ steps.pip-cache.outputs.dir }}
-        key: ${{ runner.os }}-${{ matrix.python-version }}-pythonpip
-
     - name: Install mip for testing (PyPy)
       if: ${{ matrix.python-version == 'pypy3.9-v7.3.9' }}
       run: python -m pip install .[test,numpy]