[CI] Rename basic CI stage-a/b/c -> base-a/b/c for symmetry with extra CI (#25420)

.github/actions/wait-for-jobs/action.yml

@@ -3,12 +3,12 @@ description: Poll and wait for specified jobs in the current workflow run to com
 
 inputs:
   stage-name:
-    description: 'Human-readable stage name for log messages (e.g. "stage-a")'
+    description: 'Human-readable stage name for log messages (e.g. "base-a")'
     required: true
   jobs:
     description: |
       JSON array of job specs to wait for. Each element is either:
-        - a string: exact job name (e.g. "stage-a-test-1-gpu-small")
+        - a string: exact job name (e.g. "base-a-test-1-gpu-small")
         - an object { "prefix": "...", "expected_count": N }: for matrix jobs
     required: true
   max-wait-minutes: