Use the branch name "main" for the IL2CPP repo in the il2cpp-deps update

This job updates the Mono version in the il2cpp-deps Stevedore artifact.
It should use the new main branch name in the IL2CPP repo.

.yamato/Update Il2cpp-deps.yml

@@ -9,7 +9,7 @@ commands:
   - |
     git clone [email protected]:unity/prtools.git
     cd prtools
-    git checkout master
+    git checkout main
     cmd /c cibuildscript
     cmd /c xcopy build %PRTOOLS_BUILD_DIR% /s /Y /E /I
     cd %UNITY_SOURCE_PRTOOLS_DIR%