Add julia-actions/cache to docs building in CI

Author: abhro

.github/workflows/CI.yml

@@ -48,6 +48,7 @@ jobs:
       - uses: julia-actions/setup-julia@v2
         with:
           version: "1.11"
+      - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-docdeploy@releases/v1
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}