Update spellcheck.yml

Hardcodes the Ubuntu version to get around a warning on the GitHub dashboard, will be removed after actions/runner-images#10636 is completed

.github/workflows/spellcheck.yml

@@ -9,7 +9,7 @@ jobs:
     # run on all push events or on PR syncs not from the same repo
     if: github.event_name != 'pull_request' || github.repository != github.event.pull_request.head.repo.full_name
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4