Fix command injection vulnerability in test-failure-analysis.yml

Prevent command injection by passing untrusted GitHub context values
(workflow_run.name and workflow_run.head_branch) through environment
variables instead of direct shell interpolation.

The vulnerability allowed malicious branch names with shell metacharacters
like $() to execute arbitrary commands. Now these values are safely passed
as environment variables which prevents shell expansion.

Fixes: HIGH severity command injection vulnerability on lines 66-67, 92

examples/test-failure-analysis.yml

@@ -53,6 +53,8 @@ jobs:
           fromJSON(steps.detect.outputs.structured_output).confidence >= 0.7
         env:
           GH_TOKEN: ${{ github.token }}
+          WORKFLOW_NAME: ${{ github.event.workflow_run.name }}
+          HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
         run: |
           OUTPUT='${{ steps.detect.outputs.structured_output }}'
           CONFIDENCE=$(echo "$OUTPUT" | jq -r '.confidence')
@@ -63,8 +65,7 @@ jobs:
           echo ""
           echo "Triggering automatic retry..."
 
-          gh workflow run "${{ github.event.workflow_run.name }}" \
-            --ref "${{ github.event.workflow_run.head_branch }}"
+          gh workflow run "$WORKFLOW_NAME" --ref "$HEAD_BRANCH"
 
       # Low confidence flaky detection - skip retry
       - name: Low confidence detection
@@ -83,13 +84,14 @@ jobs:
         if: github.event.workflow_run.event == 'pull_request'
         env:
           GH_TOKEN: ${{ github.token }}
+          HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
         run: |
           OUTPUT='${{ steps.detect.outputs.structured_output }}'
           IS_FLAKY=$(echo "$OUTPUT" | jq -r '.is_flaky')
           CONFIDENCE=$(echo "$OUTPUT" | jq -r '.confidence')
           SUMMARY=$(echo "$OUTPUT" | jq -r '.summary')
 
-          pr_number=$(gh pr list --head "${{ github.event.workflow_run.head_branch }}" --json number --jq '.[0].number')
+          pr_number=$(gh pr list --head "$HEAD_BRANCH" --json number --jq '.[0].number')
 
           if [ -n "$pr_number" ]; then
             if [ "$IS_FLAKY" = "true" ]; then