fix: use array format for self-hosted runners at org level

Changed runs-on from 'local-ubuntu-latest' to '[self-hosted, local-ubuntu-latest]'
to properly match organization-level ARC runner scale sets.

For organization-level runners, GitHub Actions requires the self-hosted
label along with the runner scale set name.

.github/workflows/ci.yaml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   lint-and-test:
-    runs-on: local-ubuntu-latest
+    runs-on: [self-hosted, local-ubuntu-latest]
     timeout-minutes: 10
 
     steps:

.github/workflows/prepare-release.yaml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   prepare:
-    runs-on: local-ubuntu-latest
+    runs-on: [self-hosted, local-ubuntu-latest]
     steps:
       - name: Validate version format
         run: |