Fix branch of badges in readme #39

Job	Run time
binary (humble, main) / humble main	1m 58s
binary (humble, testing) / humble testing	1m 47s
binary (iron, main) / iron main	1m 43s
binary (iron, testing) / iron testing	1m 46s
binary (rolling, main) / rolling main	1m 51s
binary (rolling, testing) / rolling testing	2m 7s
	11m 12s

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