Pull the builder image on every run

The runner caches :latest, so image updates (squashfs-tools, love-dist
cache) never reached the steps without pull: true.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

example-woodpecker.yaml

@@ -7,11 +7,13 @@ steps:
 
   - name: export
     image: git.teletypegames.org/internal/love-builder:latest
+    pull: true
     commands:
       - make ci-export
 
   - name: binaries
     image: git.teletypegames.org/internal/love-builder:latest
+    pull: true
     commands:
       - make ci-binaries