gha: invalidate .nox cache

Similar to d4482b7

Author: efiop

.github/workflows/tests.yml

@@ -42,7 +42,7 @@ jobs:
       uses: actions/cache@v3
       with:
         path: .nox
-        key: ${{ runner.os }}-${{ matrix.pyv }}-${{ hashFiles('noxfile.py') }}_nox2
+        key: ${{ runner.os }}-${{ matrix.pyv }}-${{ hashFiles('noxfile.py') }}_nox3
 
     - name: cache pre-commit hook
       uses: actions/cache@v3