Upgrade GitHub Actions for Node 24 compatibility (#9692)

Summary:
Upgrade GitHub Actions to their latest versions to ensure compatibility with Node 24, as Node 20 will reach end-of-life in April 2026.

## Changes

| Action | Old Version(s) | New Version | Release | Files |
|--------|---------------|-------------|---------|-------|
| `actions/checkout` | [`v3`](https://github.com/actions/checkout/releases/tag/v3) | [`v6`](https://github.com/actions/checkout/releases/tag/v6) | [Release](https://github.com/actions/checkout/releases/tag/v6) | ubuntu.yml |
| `actions/upload-artifact` | [`v3`](https://github.com/actions/upload-artifact/releases/tag/v3) | [`v6`](https://github.com/actions/upload-artifact/releases/tag/v6) | [Release](https://github.com/actions/upload-artifact/releases/tag/v6) | ubuntu.yml |

## Context

Per [GitHub's announcement](https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/), Node 20 is being deprecated and runners will begin using Node 24 by default starting March 4th, 2026.

### Why this matters

- **Node 20 EOL**: April 2026
- **Node 24 default**: March 4th, 2026
- **Action**: Update to latest action versions that support Node 24

### Security Note

Actions that were previously pinned to commit SHAs remain pinned to SHAs (updated to the latest release SHA) to maintain the security benefits of immutable references.

### Testing

These changes only affect CI/CD workflow configurations and should not impact application functionality. The workflows should be tested by running them on a branch before merging.

Pull Request resolved: #9692

Reviewed By: Wilfred

Differential Revision: D89277332

fbshipit-source-id: 813aa086a1954a419cc16e7076e5f3bc17196cd1

Author: salmanmkc

.github/workflows/ubuntu.yml

@@ -59,13 +59,13 @@ jobs:
         update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-${CLANG_VERSION} 500
         update-alternatives --set c++ /usr/bin/clang++-${CLANG_VERSION}
     - name: Fetching HHVM and its submodules
-      uses: actions/checkout@v3
+      uses: actions/checkout@v6
       with:
         submodules: 'recursive'
     - name: Installing HHVM deps and building HHVM
       run: ci/bin/make-debianish-package
     - name: Uploading artifacts
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v6
       with:
         name: out-directory
         path: ${{ env.OUT }}