fix(ci): add workflow_dispatch trigger to minio tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: npow

.github/workflows/metaflow.s3_tests.minio.yml

@@ -10,6 +10,7 @@ on:
       - opened
       - synchronize
       - labeled
+  workflow_dispatch:
 
 permissions: read-all