update runner name and checkout version

Signed-off-by: Basil Bruhn <basil.bruhn@psi.ch>

.gitea/workflows/webhosting-dmz.yaml

@@ -10,9 +10,9 @@ on:
 
 jobs:
   validate:
-    runs-on: webhosting
+    runs-on: webhosting_dmz
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v7
         with:
           persist-credentials: false
       - name: Lint and check Compose syntax