[NFC][clang-tools-extra] Inclusive language: replace master with main

[NFC] As part of using inclusive language within the llvm project, this patch
replaces master with main in `SubModule2.h`.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D114100

GitOrigin-RevId: c3dc6b081da6ba503e67d260033f81f61eb38ea3
diff --git a/test/modularize/SubModule2.h b/test/modularize/SubModule2.h
index 70d711b..b2e5a62 100644
--- a/test/modularize/SubModule2.h
+++ b/test/modularize/SubModule2.h
@@ -1,3 +1,3 @@
-// SubModule2.h - Master header with same name as directory.
+// SubModule2.h - Main header with same name as directory.
 #include "SubModule2/Header3.h"
 #include "SubModule2/Header4.h"