chore: update actions/cache to version 6.0.0 in deploy_mkdocs.yml

Author: mwirikia

.github/workflows/deploy_mkdocs.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           python-version: 3.x
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
-      - uses: actions/cache@13aacd865c20de90d75de3b17ebe84f7a17d57d2 # v4.0.0
+      - uses: actions/cache@2c8a9bd7457de244a408f35966fab2fb45fda9c8 # v6.0.0
         with:
           key: mkdocs-material-${{ env.cache_id }}
           path: .cache