build

Add mutex_m gem to development dependencies #301

Job	Run time
test (3.1, ACTIVE_RECORD_VERSION="~> 7.0.0", false)	44s
test (3.1, ACTIVE_RECORD_VERSION="~> 7.1.0", false)	49s
test (3.1, ACTIVE_RECORD_VERSION="~> 7.2.0", false)	49s
test (3.2, ACTIVE_RECORD_VERSION="~> 7.0.0", false)	42s
test (3.2, ACTIVE_RECORD_VERSION="~> 7.1.0", false)	42s
test (3.2, ACTIVE_RECORD_VERSION="~> 7.2.0", false)	46s
test (3.2, ACTIVE_RECORD_VERSION="~> 8.0.0", false)	44s
test (3.3, ACTIVE_RECORD_VERSION="~> 7.0.0", false)	45s
test (3.3, ACTIVE_RECORD_VERSION="~> 7.1.0", false)	44s
test (3.3, ACTIVE_RECORD_VERSION="~> 7.2.0", false)	44s
test (3.3, ACTIVE_RECORD_VERSION="~> 8.0.0", false)	46s
test (3.4, ACTIVE_RECORD_VERSION="~> 7.0.0", false)	1m 48s
test (3.4, ACTIVE_RECORD_VERSION="~> 7.1.0", false)	1m 46s
test (3.4, ACTIVE_RECORD_VERSION="~> 7.2.0", false)	1m 43s
test (3.4, ACTIVE_RECORD_VERSION="~> 8.0.0", false)	1m 41s
test (3.4, ACTIVE_RECORD_BRANCH="main", true)	1m 52s
test (3.4, ACTIVE_RECORD_BRANCH="8-0-stable", true)	1m 46s
test (3.4, ACTIVE_RECORD_BRANCH="7-2-stable", true)	1m 49s
test (3.4, ACTIVE_RECORD_BRANCH="7-1-stable", true)	1m 49s
test (3.4, ACTIVE_RECORD_BRANCH="7-0-stable", true)	1m 44s
	24m 13s

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