Use arm runner on arm kernel builds (tinkerbell#12)

## Description



Fixes: #

## How Has This Been Tested?





## How are existing users impacted? What migration steps/scripts do we need?





## Checklist:

I have:

- [ ] updated the documentation and/or roadmap (if required)
- [ ] added unit or e2e tests
- [ ] provided instructions on how to upgrade

Author: mergify[bot]

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
             mainline_runner: '{"group":"Default","labels":["oracle-vm-16cpu-64gb-x86-64"]}'
           - arch: arm64
             fork_runner: ubuntu-24.04-arm
-            mainline_runner: '{"group":"Default","labels":["oracle-vm-16cpu-64gb-x86-64"]}'
+            mainline_runner: '{"group":"Default","labels":["oracle-vm-16cpu-64gb-arm64"]}'
     env:
       ARCH: ${{ matrix.arch }}
       KERNEL_MODE: docker