Use ubuntu-latest for all GH actions runners (#33473)

.github/workflows/check-i18n.yml

@@ -18,7 +18,7 @@ permissions:
 
 jobs:
   check-i18n:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v4

.github/workflows/test-ruby.yml

@@ -174,7 +174,7 @@ jobs:
 
   test-libvips:
     name: Libvips tests
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-latest
 
     needs:
       - build