Disable run-ui in contributor workflow

Seems to be another intermittent issue with downloading Gradle. 

```Kotlin
Downloading https://services.gradle.org/distributions/gradle-7.0.2-all.zip
WARNING | /etc/localtime does not point to zoneinfo-compatible timezone name

Exception in thread "main" java.net.SocketException: Broken pipe (Write failed)
```

.github/workflows/build-contributor-pr.yml

@@ -107,7 +107,7 @@ jobs:
 
   run-ui:
     runs-on: macos-11
-    if: github.event.pull_request.head.repo.full_name != github.repository && github.actor != 'MickeyMoz'
+    if: ${{ false }}
 
     timeout-minutes: 60
     strategy: