[backport] Bump julia-actions/cache to v3 (#14412)

v2 is a composite action whose post-save and delete-old-caches steps
don't run reliably, letting per-run julia caches (~250 MB each)
accumulate on refs/heads/main until the repository hits its 10 GB
cache cap. v3 is a JavaScript rewrite with a proper post hook. It also
uses Node.js 24 directly, dropping the latent Node 20 exposure from
v2's transitive actions/cache dependency.

Author: cderv

.github/workflows/test-smokes.yml

@@ -223,7 +223,7 @@ jobs:
           version: "1.11.7"
 
       - name: Load Julia packages from cache
-        uses: julia-actions/cache@v2
+        uses: julia-actions/cache@v3
         with:
           cache-name: julia-cache;workflow=${{ github.workflow }};job=${{ github.job }};julia=${{ steps.setup-julia.outputs.julia-version }}