fix: prevent command injection in test-failure-analysis example

Fix command injection vulnerability where github.event.workflow_run.head_branch
was directly interpolated into shell commands. Branch names containing shell
metacharacters could execute arbitrary commands.

Changes:
- Pass head_branch through environment variables instead of direct interpolation
- Affects gh pr list --head and gh workflow run --ref commands
- Prevents execution of malicious code in branch names

Severity: HIGH
Category: command_injection

examples/test-failure-analysis.yml

@@ -53,7 +53,6 @@ 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 }}'
@@ -65,7 +64,8 @@ jobs:
           echo ""
           echo "Triggering automatic retry..."
 
-          gh workflow run "$WORKFLOW_NAME" --ref "$HEAD_BRANCH"
+          gh workflow run "${{ github.event.workflow_run.name }}" \
+            --ref "$HEAD_BRANCH"
 
       # Low confidence flaky detection - skip retry
       - name: Low confidence detection