Update time parsing in `merge-tops-bursts.py` #816

Job	Run time
call-version-info-workflow / version_info	1m 6s
call-pytest-workflow / pytest (3.10)	1m 41s
call-pytest-workflow / pytest (3.11)	1m 42s
call-docker-ghcr-workflow / dockerize	3m 47s
	8m 16s

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