chore(deps): pin actions/cache action to 6849a64 (#300)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/build-and-test.yaml

@@ -58,7 +58,7 @@ jobs:
 
       - name: Cache wheels
         id: cache-wheels
-        uses: actions/cache@v4
+        uses: actions/cache@6849a6489940f00c2f30c0fb92c6274307ccb58a # v4
         with:
           path: /home/runner/snap/charmcraft/common/cache/charmcraft
           key: ${{ runner.os }}-wheel-cache-${{ hashFiles('./uv.lock') }}