CI: all Linux jobs of main and merge-queue runs use the self-hosted runner (#1864)

Only the Windows jobs still wait for GitHub's runners on main and in the
merge queue. The Vulkan packages are preinstalled on the self-hosted
runner (no sudo), so that step runs only on GitHub-hosted runners.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -53,7 +53,7 @@ jobs:
 
   changes:
     name: Select checks
-    runs-on: ubuntu-24.04
+    runs-on: ${{ github.event_name == 'pull_request' && 'ubuntu-24.04' || 'self-hosted-fast' }}
     outputs:
       native: ${{ steps.paths.outputs.native }}
       kernel: ${{ steps.paths.outputs.kernel }}
@@ -105,7 +105,7 @@ jobs:
 
   checks:
     name: Format and repository checks
-    runs-on: ubuntu-24.04
+    runs-on: ${{ github.event_name == 'pull_request' && 'ubuntu-24.04' || 'self-hosted-fast' }}
     timeout-minutes: 15
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -209,7 +209,7 @@ jobs:
   tests:
     name: Native Linux tests (${{ matrix.shard }}/4)
     needs: [changes, build-tests]
-    runs-on: ubuntu-24.04
+    runs-on: ${{ github.event_name == 'pull_request' && 'ubuntu-24.04' || 'self-hosted-fast' }}
     timeout-minutes: 60
     strategy:
       fail-fast: false
@@ -224,6 +224,8 @@ jobs:
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
       - name: Install a software Vulkan driver (lavapipe)
+        # Preinstalled on the self-hosted runner, which has no sudo.
+        if: runner.environment == 'github-hosted'
         run: |
           sudo apt-get update
           sudo apt-get install -y --no-install-recommends mesa-vulkan-drivers libvulkan1
@@ -391,7 +393,7 @@ jobs:
     name: Reference tests
     needs: changes
     if: needs.changes.outputs.native == 'true'
-    runs-on: ubuntu-24.04
+    runs-on: ${{ github.event_name == 'pull_request' && 'ubuntu-24.04' || 'self-hosted-fast' }}
     timeout-minutes: 60
     env:
       CARGO_INCREMENTAL: "0"
@@ -478,7 +480,7 @@ jobs:
   ci:
     needs: [changes, checks, clippy, build-tests, tests, doc-tests, oracle, windows-fxc, windows-startup]
     if: always()
-    runs-on: ubuntu-24.04
+    runs-on: ${{ github.event_name == 'pull_request' && 'ubuntu-24.04' || 'self-hosted-fast' }}
     steps:
       - name: Verify required checks
         env: