dev-inf: Add Vertex AI environment variables to Claude Code action

The Claude Code action requires ANTHROPIC_VERTEX_PROJECT_ID and
CLOUD_ML_REGION to be set when using Vertex AI. Added these
environment variables to all four action steps.

Release note: None
Epic: None

Author: ajstorm

.github/workflows/pr-analyzer-threestage.yml

@@ -29,6 +29,9 @@ jobs:
       - name: Stage 1 - Initial Bug Screening
         id: stage1
         uses: cockroachdb/claude-code-action@v1
+        env:
+          ANTHROPIC_VERTEX_PROJECT_ID: vertex-model-runners
+          CLOUD_ML_REGION: global
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           use_vertex: "true"
@@ -64,6 +67,9 @@ jobs:
         id: stage2
         if: contains(steps.stage1.outputs.result, 'STAGE1_RESULT - POTENTIAL_BUG_DETECTED')
         uses: cockroachdb/claude-code-action@v1
+        env:
+          ANTHROPIC_VERTEX_PROJECT_ID: vertex-model-runners
+          CLOUD_ML_REGION: global
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           use_vertex: "true"
@@ -100,6 +106,9 @@ jobs:
         id: stage3
         if: contains(steps.stage2.outputs.result, 'STAGE2_RESULT - POTENTIAL_BUG_DETECTED')
         uses: cockroachdb/claude-code-action@v1
+        env:
+          ANTHROPIC_VERTEX_PROJECT_ID: vertex-model-runners
+          CLOUD_ML_REGION: global
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           use_vertex: "true"
@@ -150,6 +159,9 @@ jobs:
       - name: Final Analysis Report
         if: always()
         uses: cockroachdb/claude-code-action@v1
+        env:
+          ANTHROPIC_VERTEX_PROJECT_ID: vertex-model-runners
+          CLOUD_ML_REGION: global
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           use_vertex: "true"