LAKITU: make repohooks compatible with older COS branches

BUG=b/277779682
TEST=Upload change on M93
RELEASE_NOTE=None

Change-Id: I96c921e471e6d196548e3059e10f4d59e45d6798
Reviewed-on: https://cos-review.googlesource.com/c/cos/repohooks/+/50870
Reviewed-by: He Gao <hegao@google.com>
Tested-by: Robert Kolchmeyer <rkolchmeyer@google.com>

pre-upload.py

diff --git a/pre-upload.py b/pre-upload.py
index 3eae70d..ab069e6 100755
--- a/pre-upload.py
+++ b/pre-upload.py
@@ -54,7 +54,13 @@
 
 # The sys.path monkey patching confuses the linter.
 # pylint: disable=wrong-import-position
-from chromite.format import formatters
+
+# lakitu: older branches do not have this dependency. The things that depend on
+# it don't exist either, so we can ignore this import failure.
+try:
+    from chromite.format import formatters
+except ImportError:
+    pass
 from chromite.lib import commandline
 from chromite.lib import constants
 from chromite.lib import cros_build_lib