Swap all self-hosted runners to ubuntu-latest per b/451586626 (#11023)

.github/workflows/release-manual.yml

@@ -46,7 +46,7 @@ on:
 
 jobs:
   release:
-    runs-on: 'self-hosted'
+    runs-on: 'ubuntu-latest'
     permissions:
       contents: 'write'
       packages: 'write'

.github/workflows/smoke-test.yml

@@ -20,7 +20,7 @@ on:
 
 jobs:
   smoke-test:
-    runs-on: 'self-hosted'
+    runs-on: 'ubuntu-latest'
     permissions:
       contents: 'read'
       issues: 'write'

.github/workflows/stale.yml

@@ -13,7 +13,6 @@ jobs:
       matrix:
         runner:
           - 'ubuntu-latest' # GitHub-hosted
-          - 'self-hosted' # GHA on GCP runners
     runs-on: '${{ matrix.runner }}'
     if: |-
       ${{ github.repository == 'google-gemini/gemini-cli' }}