ci: Update extension-validation enabling caching of python dependencies

See https://github.com/actions/setup-python/blob/main/docs/advanced-usage.md#caching-packages

Author: jcfr

.github/workflows/extension-validation.yml

@@ -26,6 +26,8 @@ jobs:
       - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
         with:
           python-version: "3.12"
+          cache: "pip"
+          cache-dependency-path: scripts/requirements.txt
 
       - name: Configure git
         run: |