Do version specific cashing for tox. Use correct path.

.github/workflows/tox.yml

@@ -31,10 +31,10 @@ jobs:
     - name: tox env cache
       uses: actions/cache@v2
       with:
-        path: ./.tox
-        key: ${{ runner.os }}-tox-${{ hashFiles('**/requirements/*.txt') }}
+        path: ${{ github.workspace }}/.tox/py${{ matrix.python-version }}
+        key: ${{ runner.os }}-tox-py${{ matrix.python-version }}-${{ hashFiles('**/requirements/*.txt') }}
         restore-keys: |
-          ${{ runner.os }}-tox-
+          ${{ runner.os }}-tox-py${{ matrix.python-version }}
     - name: Test with tox
       run: tox -e py${{ matrix.python-version }}
   postgres:
@@ -79,9 +79,9 @@ jobs:
     - name: tox env cache
       uses: actions/cache@v2
       with:
-        path: ./.tox
-        key: ${{ runner.os }}-tox-${{ hashFiles('**/requirements/*.txt') }}
+        path: ${{ github.workspace }}/.tox/py${{ matrix.python-version }}
+        key: ${{ runner.os }}-tox-py${{ matrix.python-version }}-${{ hashFiles('**/requirements/*.txt') }}
         restore-keys: |
-          ${{ runner.os }}-tox-
+          ${{ runner.os }}-tox-py${{ matrix.python-version }}
     - name: Test with tox
       run: tox -e postgres