Add `shared_context` for Rails 8.1 #546

Job	Run time
Check documentation syntax	16s
Spec - JRuby	1m 34s
Spec - 2.7	32s
Check the oldest supported RuboCop version	28s
Prism	31s
Spec - 3.0	49s
Spec - 3.1	51s
Spec - 3.2	18s
Spec - 3.3	16s
Spec - 3.4	14s
Spec - head	22s
	6m 11s

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