ci: route to canonical native arcd labels [self-hosted, linux, <arch>]

Replaces non-canonical scale-set / org-prefixed labels with the
existing labels every arcd host registers with. Matches evo for
amd64 and spark for arm64. No new labels added.

.github/workflows/build-lux.yml

@@ -31,7 +31,7 @@ env:
 
 jobs:
   build:
-    runs-on: lux-build-linux-amd64
+    runs-on: [self-hosted, linux, amd64]
     permissions:
       contents: read
       packages: write
@@ -80,7 +80,7 @@ jobs:
   deploy:
     needs: build
     if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request'
-    runs-on: lux-build-linux-amd64
+    runs-on: [self-hosted, linux, amd64]
     permissions:
       contents: read
     steps: