ci: upgrade astral-sh/ruff-action to v4.0.0

Updates 2 occurrences across 1 workflow file from v3 to v4.0.0.
v4.0.0 runs on Node 24; v3 runs on Node 20 which is
being deprecated on GitHub Actions runners.

See https://github.com/astral-sh/ruff-action/releases/tag/v4.0.0

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: andrewhsu

.github/workflows/lint-python.yml

@@ -22,12 +22,12 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v6
       - name: Ruff format --check
-        uses: astral-sh/ruff-action@v3
+        uses: astral-sh/ruff-action@v4.0.0
         with:
           args: "format --check --diff"
           version: "0.12.10"
       - name: Ruff check (/tests only)
-        uses: astral-sh/ruff-action@v3
+        uses: astral-sh/ruff-action@v4.0.0
         with:
           args: "check --output-format=github"
           src: "./tests"