GitHub CI: Use a bigger builder for x86_64-linux

Also, don't use a matrix for the 'tests' workflow, since we don't want
the 'vm_tests' and 'flake_regressions' workflows to depend on
aarch64-darwin.

.github/workflows/ci.yml

@@ -10,23 +10,18 @@ permissions:
 
 jobs:
 
-  tests:
+  test_x86_64-linux:
-    strategy:
+    uses: ./.github/workflows/test.yml
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest, macos-latest]
-    runs-on: ${{ matrix.os }}
-    timeout-minutes: 60
-    steps:
-      - uses: actions/checkout@v4
-      - uses: DeterminateSystems/nix-installer-action@main
     with:
-          flakehub: true
+      os: UbuntuLatest32Cores128G
-      - uses: DeterminateSystems/magic-nix-cache-action@main
+
-      - run: nix flake check -L
+  test_aarch64-darwin:
+    uses: ./.github/workflows/test.yml
+    with:
+      os: macos-latest
 
   vm_tests:
-    needs: tests
+    needs: test_x86_64-linux
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -37,7 +32,7 @@ jobs:
       - run: nix build -L .#hydraJobs.tests.githubFlakes .#hydraJobs.tests.tarballFlakes
 
   flake_regressions:
-    needs: tests
+    needs: test_x86_64-linux
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout nix

.github/workflows/test.yml

@@ -0,0 +1,21 @@
+on:
+  workflow_call:
+    inputs:
+      os:
+        required: true
+        type: string
+
+jobs:
+
+  tests:
+    strategy:
+      fail-fast: false
+    runs-on: ${{ inputs.os }}
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@v4
+      - uses: DeterminateSystems/nix-installer-action@main
+        with:
+          flakehub: true
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - run: nix flake check -L