Fix setup-uv action version to v6

Author: jurgelenas

.github/workflows/lint.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
-      - uses: astral-sh/setup-uv@v8
+      - uses: astral-sh/setup-uv@v6
       - run: uv sync
       - run: uv run ruff check rfmeter/
       - run: uv run ruff format --check rfmeter/