ci: use a specific ubuntu version

GHA shows a warning telling that "ubuntu-latest" is going to be switched
to ubuntu-24.04 soon. Let's specify the version explicitly (and switch
to 24.04 for this job ahead of github).

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

.github/workflows/validate.yml

@@ -127,7 +127,7 @@ jobs:
         run : ./script/check-config.sh
 
   space-at-eol:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
       - run: rm -fr vendor