Prefer interpolation to array join #406

Job	Run time
Ruby specs (2.6, rails_6.0, stable)	2m 1s
Ruby specs (2.6, rails_6.1, stable)	2m 25s
Ruby specs (2.7, rails_6.0, stable)	2m 3s
Ruby specs (2.7, rails_6.1, stable)	1m 53s
Ruby specs (2.7, rails_7.0, stable)	2m 30s
Ruby specs (3.0, rails_6.0, stable)	1m 43s
Ruby specs (3.0, rails_6.1, stable)	1m 41s
Ruby specs (3.0, rails_7.0, stable)	1m 41s
Ruby specs (3.1, rails_7.0, stable)	1m 43s
Ruby specs (3.2, rails_7.0, stable)	1m 39s
Ruby specs (2.7, rails_edge, experimental)	2m 13s
Ruby specs (3.0, rails_edge, experimental)	1m 48s
Ruby specs (3.1, rails_edge, experimental)	1m 54s
Ruby specs (3.2, rails_edge, experimental)	1m 53s
Ruby specs (head, rails_7.0, experimental)	1m 48s
Ruby specs (head, rails_edge, experimental)	1m 43s
	30m 38s

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