workflows: use ARM runners

ARM runners are supposed to be more energy efficient than x86. Also,
from limited testing, they appear to be faster for the eval jobs as
well. Average run time for the "Outpaths (x86_64-linux)" job was 4m 27s,
so far. In the first run, this job came in at 3m 9s. This effect did not
show for other jobs, yet.

The following two exceptions are made right now:
- nixpkgs-lib-tests currently fails on the ARM runner building Nix 2.3
- nixpkgs-vet is currently pinned to a x86_64-linux only binary release

.github/workflows/codeowners-v2.yml

@@ -41,7 +41,7 @@ jobs:
   # Check that code owners is valid
   check:
     name: Check
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-24.04-arm
     needs: get-merge-commit
     if: github.repository_owner == 'NixOS' && needs.get-merge-commit.outputs.mergedSha
     steps:
@@ -89,7 +89,7 @@ jobs:
   # Request reviews from code owners
   request:
     name: Request
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-24.04-arm
     if: github.repository_owner == 'NixOS'
     steps:
       - uses: cachix/install-nix-action@526118121621777ccd86f79b04685a9319637641 # v31