compat: fix format_changeset_summary_fn() for hg <= 5.6

8 jobs for topic/default/missing-return in 4 minutes and 21 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
passed checks-py2 #158343

00:02:16

passed checks-py3 #158344

00:02:35

passed doc #158349

00:00:43

manual pytype #158342
allowed to fail manual
passed tests-py2-cext #158345

00:04:13

passed tests-py2-pure #158346

00:03:47

passed tests-py3-cext #158347

00:04:21

passed tests-py3-pure #158348

00:04:11