fix(test-classifier): point reusable workflow at fetch-skills.sh

The agent-skills migration (#41) renamed sync-skills.sh -> fetch-skills.sh
and changed its behavior to vendor SKILL.md from navapbc/agent-skills into
.skills-vendor/, but the reusable workflow's setup step was never updated.
It chmod'd and ran the nonexistent sync-skills.sh, aborting every consumer
run under `set -euo pipefail`:

  chmod: cannot access 'testing/classifier/scripts/sync-skills.sh': No such file or directory

Update both references to fetch-skills.sh, rename the step to describe what
it actually does, and drop the no-op AI_REVIEW_TOOL env (fetch-skills.sh
doesn't read it; the var is still used by the classifier run step).

Author: fg-nava

.github/workflows/test-classifier.yml

@@ -196,13 +196,11 @@ jobs:
           cp -R .classifier-bundle/testing "$GITHUB_WORKSPACE/testing"
           chmod +x testing/classifier/.skills/_lib/ai-classifier-dispatch.sh
           chmod +x testing/classifier/.skills/test-classifier/scripts/test-classifier-dispatcher.sh
-          chmod +x testing/classifier/scripts/sync-skills.sh
+          chmod +x testing/classifier/scripts/fetch-skills.sh
 
-      - name: Sync canonical SKILL.md into the chosen tool's directory
+      - name: Vendor SKILL.md from agent-skills
         working-directory: testing/classifier
-        env:
-          AI_REVIEW_TOOL: ${{ inputs.tool }}
-        run: scripts/sync-skills.sh
+        run: scripts/fetch-skills.sh
 
       # ── Bedrock auth (provider=bedrock only) ────────────────────────────────
       # Exchange this run's GitHub OIDC token for short-lived STS credentials by