go: add missing path dependency for migration tool

The migration tool references source code in the k8s/ but the workflow
doesn't. This causes errors when `go mod tidy` is executed

Signed-off-by: Ivo Jimenez <[email protected]>

Author: ivotron

.github/workflows/redpanda-migration-build.yml

@@ -19,6 +19,7 @@ on:
     paths:
       - .github/workflows/redpanda-migration-build.yml
       - src/go/cluster-to-redpanda-migration
+      - src/go/k8s/
 
 jobs:
   test: