llvm monitor: Ignore buildkite builds of release branches

Recently 14.x builds have been popping up so it's not enough
to just ignore those triggered from Phabricator reviews.

Change-Id: I1f8fc1928ee31a9cb913f83cc45bcea2c6a4baa5
diff --git a/monitor/buildkite_status.py b/monitor/buildkite_status.py
index d2fbab9..8978ef2 100755
--- a/monitor/buildkite_status.py
+++ b/monitor/buildkite_status.py
@@ -65,10 +65,12 @@
 
     for build in builds:
         # There are two kinds of builds. Those triggered from phab reviews
-        # and those run perdidically to post-commit build the main branch.
-        # For the status page we ignore pre-commit builds.
+        # and those run perdidically to post-commit build the main and release
+        # branches.
+        # For the status page we ignore pre-commit and release builds.
         # ph_buildable_revision is set if Phabricator triggered this build.
-        if 'ph_buildable_revision' in build['env']:
+        if 'ph_buildable_revision' in build['env'] or \
+           build['branch'] != 'main':
             continue
 
         # Where each "job" is a config e.g. AArch64, MacOS, C++20 etc.