fix: Replace dynamic env.cache_id with github.run_id in workflow caches

- Eliminates 'Context access might be invalid: cache_id' warnings
- Uses built-in GitHub Actions context for better reliability
- Simplifies workflow by removing dynamic environment variable step

Author: spacelord16

.github/workflows/publish-docs-manually.yml

@@ -21,10 +21,9 @@ jobs:
           enable-cache: true
           version: 0.7.2
 
-      - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
       - uses: actions/cache@v4
         with:
-          key: mkdocs-material-${{ env.cache_id }}
+          key: mkdocs-material-${{ github.run_id }}
           path: .cache
           restore-keys: |
             mkdocs-material-

.github/workflows/publish-pypi.yml

@@ -70,10 +70,9 @@ jobs:
           enable-cache: true
           version: 0.7.2
 
-      - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
       - uses: actions/cache@v4
         with:
-          key: mkdocs-material-${{ env.cache_id }}
+          key: mkdocs-material-${{ github.run_id }}
           path: .cache
           restore-keys: |
             mkdocs-material-