Update branch name.

Change-Id: Ib14950553f92bb5cd1baccda2534d52338f8ba39
diff --git a/copybara/copy.bara.sky b/copybara/copy.bara.sky
index 6c2d036..54ca37c 100644
--- a/copybara/copy.bara.sky
+++ b/copybara/copy.bara.sky
@@ -2,7 +2,7 @@
     name = "default",
     origin = git.origin(
         url = "https://github.com/llvm/llvm-project.git",
-        ref = "master",
+        ref = "main",
     ),
     origin_files = glob(
         [