CI: revert unity-tests.yml to upstream/main version

Author: dsarno

.github/workflows/unity-tests.yml

@@ -7,7 +7,6 @@ on:
       - TestProjects/UnityMCPTests/**
       - UnityMcpBridge/Editor/**
       - .github/workflows/unity-tests.yml
-  workflow_dispatch:
 
 jobs:
   testAllModes: