Add upgrade pip step to workflow

Author: mikemanger

.github/workflows/tests.yml

@@ -19,6 +19,8 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
-      run: pip install tox tox-gh
+      run: |
+        python -m pip install --upgrade pip
+        pip install tox tox-gh
     - name: Test with tox
       run: tox -e ${{ matrix.python-version }}