Fix CI lint: install ruff instead of black/isort in PR workflow

The Makefile's check-format target now uses `ruff format` but CI was
still installing black, isort, and linecheck, causing "ruff: No such
file or directory".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MaxGhenis

.github/workflows/pr_code_changes.yaml

@@ -16,7 +16,7 @@ jobs:
         uses: astral-sh/setup-uv@v5
       - name: Install relevant dependencies
         run: |
-          uv pip install black isort linecheck --system
+          uv pip install "ruff>=0.9.0" --system
       - name: Check code formatting
         run: make check-format