llvmbot monitor: Restrict builds list to main branch

We used to ask for all builds and filter from there, but now
that pre-commit llvm PRs are doing many more builds, we aren't
finding a finished main build in the 100 entries we get back
by default.

Instead of filtering afterwards, change the initial query to be
main only.

It's still possible there would be 100 builds without a finished
one, but if that ever happens we can make use of the pagination
feature to get more until we find one.

Change-Id: Ia9e5d090ad86c8257b14be0a2dd81f1237b9233a
diff --git a/monitor/buildkite_status.py b/monitor/buildkite_status.py
index 3f9924b..39706c8 100755
--- a/monitor/buildkite_status.py
+++ b/monitor/buildkite_status.py
@@ -54,6 +54,11 @@
         pipeline,
         # Finished means passed, failed, blocked or cancelled
         states=[BuildState.FINISHED],
+        # There are two kinds of builds. Those triggered from phab reviews
+        # and those run perdidically to post-commit build the main and release
+        # branches.
+        # For the status page we ignore pre-commit and release builds.
+        branch="main",
     )
 
 
@@ -65,14 +70,6 @@
     builds = get_pipeline_builds(organisation, pipeline)
 
     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 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"] or build["branch"] != "main":
-            continue
-
         # Where each "job" is a config e.g. AArch64, MacOS, C++20 etc.
         for job in build["jobs"]:
             # Some jobs won't have a name. I think these are the wait steps