Add corral fetch step to pony-lint workflow

Projects with dependencies need corral fetch before pony-lint
can resolve their use statements.

Author: SeanTAllen

.github/workflows/pony-lint.yml

@@ -20,5 +20,7 @@ jobs:
       image: ghcr.io/ponylang/shared-docker-ci-standard-builder:release
     steps:
       - uses: actions/checkout@v6.0.2
+      - name: Fetch dependencies
+        run: corral fetch
       - name: Lint
         run: pony-lint