Run the the pre-commit CI job on ubuntu-slim

The `ubuntu-slim` runner is lighter weight, being a container
rather than using a whole VM, and having only one vCPU, less RAM,
and a 15 minute time limit. It's not suitable for most of our CI
jobs in GitPython, but it should work well for our `pre-commit`
checks. (If it doesn't, that's reason to suspect they might be
better removed from `pre-commit` and run in a different way.)

- https://github.blog/changelog/2026-01-22-1-vcpu-linux-runner-now-generally-available-in-github-actions/
- https://github.com/actions/runner-images/blob/main/images/ubuntu-slim/ubuntu-slim-Readme.md

Author: EliahKagan

.github/workflows/lint.yml

@@ -7,7 +7,7 @@ permissions:
 
 jobs:
   lint:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
 
     steps:
     - uses: actions/checkout@v6