Change the git log format and splitting logic

[damdo]

The logic here is a bit fragile and breaks when the chosen separator is contained in the commit message.

rebasebot/rebasebot/bot.py

Lines 167 to 177 in 683a41f

	commits = gitwd.git.log("--reverse", "--pretty=format:%H - %s - %aE", "--no-merges",
	"--ancestry-path", f"{merge_base}..dest/{dest.branch}")
	logging.info("Identified upstream commits:\n%s", commits)
	commits_to_squash = defaultdict(list)
	for commit in commits.splitlines():
	# Commit contains the message for logging purposes,
	# trim on the first space to get just the commit sha
	sha, commit_message, committer_email = commit.split(" - ")