actions/cache updated from v2 to v4 (#230)

Author: phanecak-maptiler

.github/cache-sources-action/action.yml

@@ -16,7 +16,7 @@ runs:
         echo "::set-output name=date::$(date -u "+%Y-%m-%d")"
       shell: bash
       working-directory: ${{ inputs.basedir }}
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       with:
         path: data/sources
         key: data-sources-${{ steps.get-data.outputs.date }}-${{ steps.get-data.outputs.hash }}