Bump CI actions to Node.js 24 native versions

actions/checkout v6, actions/upload-artifact v7 and the latest
hendrikmuhs/ccache-action v1.2.x all declare node24 in their
action metadata, so the deprecation warning that v4/v4 emit (even
under FORCE_JAVASCRIPT_ACTIONS_TO_NODE24) is gone.

Drop the FORCE_JAVASCRIPT_ACTIONS_TO_NODE24 workflow env now that
every JavaScript action used here ships native Node 24 support.

Author: Ognisty321

.github/workflows/build.yml

@@ -29,12 +29,6 @@ on:
 permissions:
   contents: read
 
-env:
-  # Opt JavaScript-based actions into Node.js 24 ahead of the
-  # GitHub-mandated 2026-06-02 cutover so we do not ship deprecation
-  # warnings on every build.
-  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: "true"
-
 concurrency:
   group: build-${{ github.ref }}
   cancel-in-progress: true
@@ -61,7 +55,7 @@ jobs:
           df -h /
 
       - name: Checkout (with submodules)
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           submodules: recursive
           fetch-depth: 1
@@ -171,7 +165,7 @@ jobs:
           } >> "$GITHUB_STEP_SUMMARY"
 
       - name: Upload kernel artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: wsa-kernel-x86_64-${{ github.run_number }}
           path: |