[skip ci] Bump actions/cache to v5 and add workflow check

Update desktop-nightly workflow to use actions/cache@v5 (targets Node 24). Update the workflow validation script to require the new action and to fail if actions/cache@v4 is still present, preventing use of the deprecated Node.js 20 runtime.

Author: zhaobozhen

.github/workflows/desktop-nightly.yml

@@ -60,7 +60,7 @@ jobs:
         uses: dtolnay/rust-toolchain@stable
 
       - name: Restore Rust build cache
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: |
             ~/.cargo/registry

scripts/check-desktop-nightly-workflow.mjs

@@ -15,6 +15,7 @@ const requiredSnippets = [
   ["manual trigger", "workflow_dispatch:"],
   ["scheduled trigger", "schedule:"],
   ["release write permission", "contents: write"],
+  ["Node 24 cache action", "actions/cache@v5"],
   ["Windows runner", "windows-latest"],
   ["macOS Apple Silicon runner", "macos-15"],
   ["macOS arm64 guard", 'test "$(uname -m)" = "arm64"'],
@@ -36,6 +37,10 @@ for (const [label, snippet] of requiredSnippets) {
   }
 }
 
+if (workflow.includes("actions/cache@v4")) {
+  fail("Desktop nightly workflow still uses actions/cache@v4, which targets the deprecated Node.js 20 runtime");
+}
+
 console.log("Checked desktop nightly workflow");
 
 function fail(message) {