repo_manifest_unittest: tweak master->main in example

The exact ref here doesn't matter, so switch it away from master.

BUG=chromium:1126855
TEST=CQ passes

Change-Id: I7ffbad0b8a1754ec36a9d8ebacdc6ca8785c46a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2701113
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Sergey Frolov <sfrolov@google.com>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
diff --git a/lib/repo_manifest_unittest.py b/lib/repo_manifest_unittest.py
index ac6e4a3..95e24d6 100644
--- a/lib/repo_manifest_unittest.py
+++ b/lib/repo_manifest_unittest.py
@@ -39,7 +39,7 @@
           fetch="http://example.com"
           pushurl="http://example.com/push"
           review="http://review.example.com"
-          revision="refs/heads/master"/>
+          revision="refs/heads/main"/>
 """
 
 DEFAULT_XML = '<default remote="simple_remote" upstream="default_upstream"/>'
@@ -48,7 +48,7 @@
 
 COMPLEX_PROJECT_XML = """
   <project name="complex/project" path="src/complex" revision="cafe"
-           remote="complex_remote" upstream="refs/heads/master">
+           remote="complex_remote" upstream="refs/heads/main">
     <annotation name="branch-mode" value="pin"/>
   </project>
 """