feat(ci): migrate all workflows to GKE self-hosted runners

Swap all `runs-on: ubuntu-latest` to `runs-on: arc-runner-set` all jobs.
The ARM docker build job in docker.yml uses `${{ matrix.runner }}`
and is left untouched since the GKE runner pool is x86_64 only.

Runners are backed by ARC (Actions Runner Controller) on a GKE cluster
with a spot preemptible node pool that scales based on job demand.

Use the baked Electron dependencies for the desktop E2E job.

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ concurrency:
 jobs:
   generate:
     name: "Generate slices"
-    runs-on: ubuntu-latest
+    runs-on: arc-runner-set
     timeout-minutes: 10
     outputs:
       matrix: ${{ steps.matrix.outputs.matrix }}
@@ -48,7 +48,7 @@ jobs:
   test:
     name: Run tests slice ${{ matrix.slice.index }}/${{ inputs.slice_count }}
     needs: generate
-    runs-on: ubuntu-latest
+    runs-on: arc-runner-set
     timeout-minutes: 30
     strategy:
       fail-fast: false
@@ -149,7 +149,7 @@ jobs:
   save-durations:
     needs: test
     if: needs.test.result == 'success' && github.ref == 'refs/heads/main'
-    runs-on: ubuntu-latest
+    runs-on: arc-runner-set
     timeout-minutes: 10
     steps:
       - name: Download all slice durations
@@ -179,7 +179,7 @@ jobs:
           key: test-durations-${{ github.run_id }}
 
   e2e:
-    runs-on: ubuntu-latest
+    runs-on: arc-runner-set
     timeout-minutes: 15
     steps:
       - name: Checkout code