Update workflow to use build-user-config.yml v0.3.0

Author: HeeTuic

.github/workflows/blank.yml

@@ -2,4 +2,4 @@ on: [push, pull_request, workflow_dispatch]
 
 jobs:
   build:
-    uses: zmkfirmware/zmk/.github/workflows/build-user-config.yml@main
+    uses: zmkfirmware/zmk/.github/workflows/build-user-config.yml@v0.3.0