ci/unitctl: Update paths

unitctl makes use of 'docs/unit-openapi.yaml' so be sure to run these
checks if that file changes.

Fixes: 6d0880c ("Add unitctl build and release CI")
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

.github/workflows/unitctl.yml

@@ -5,6 +5,7 @@ on:
   pull_request:
     paths:
       - tools/unitctl/**
+      - docs/unit-openapi.yaml
   push:
     branches:
       - master