GitHub Actions: update cache key to include interpreter path (#7835)

And make it more portable by using python

.github/workflows/python-linters.yml

@@ -56,7 +56,7 @@ jobs:
           ${{ runner.os }}-pip-
           ${{ runner.os }}-
     - name: set PY
-      run: echo "::set-env name=PY::$(python -VV | sha256sum | cut -d' ' -f1)"
+      run: echo "::set-env name=PY::$(python -c 'import hashlib, sys;print(hashlib.sha256(sys.version.encode()+sys.executable.encode()).hexdigest())')"
     - uses: actions/cache@v1
       with:
         path: ~/.cache/pre-commit