ci: upgrade actions/cache to v5.0.3

Pin actions/cache to the v5.0.3 release commit hash with a comment
holding the release number, per security best practice.

Signed-off-by: Mike Spreitzer <mspreitz@us.ibm.com>

Author: MikeSpreitzer

.github/workflows/python-code-quality.yml

@@ -21,7 +21,7 @@ jobs:
           python-version: "3.12.11"
 
       - name: Cache pip dependencies
-        uses: actions/cache@v4.2.4
+        uses: actions/cache@cdf6c1fa76f9f475f3d7449005a359c84ca0f306 # v5.0.3
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements*.txt') }}