Support arm64 in callable k0s build

Select the self-hosted arm64 runners when the architecture is arm64. The
k0s build system doesn't support cross-compilation, so the only way to
get arm64 binaries is to run on arm64.

Signed-off-by: Tom Wieczorek <[email protected]>

.github/workflows/build-k0s.yml

@@ -15,7 +15,7 @@ on:
 jobs:
   build:
     name: ${{ inputs.target-os }}-${{ inputs.target-arch }}
-    runs-on: ubuntu-22.04
+    runs-on: ${{ inputs.target-arch == 'arm64' && fromJSON('["self-hosted", "linux", "arm64"]') || 'ubuntu-22.04' }}
 
     env:
       TARGET_OS: ${{ inputs.target-os }}