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

.github/workflows/_pr-test-sgl-kernel-build.yml

@@ -24,7 +24,7 @@ on:
       git_ref:
         type: string
         default: ''
-      skip_stage_health_check:
+      skip_pr_test_health_check:
         description: 'Forwarded from the caller workflow input of the same name. Not consumed inside this reusable workflow today, but mirrored so the resulting env context matches the inline-job baseline.'
         type: boolean
         default: false
@@ -39,7 +39,7 @@ env:
   SGLANG_IS_IN_CI: true
   SGLANG_CUDA_COREDUMP: "1"
   SGLANG_JIT_DEEPGEMM_FAST_WARMUP: true
-  SKIP_STAGE_HEALTH_CHECK: ${{ inputs.skip_stage_health_check && 'true' || 'false' }}
+  SKIP_PR_TEST_HEALTH_CHECK: ${{ inputs.skip_pr_test_health_check && 'true' || 'false' }}
   FORCE_REBUILD_DEEPEP: '1'
   PR_TEST_BYPASS_MAINTENANCE_ON_MAIN: ${{ github.ref == 'refs/heads/main' && 'true' || 'false' }}
   USE_VENV: false