Add `shared_context` for Rails 8.0 #362

Job	Run time
Check documentation syntax	17s
Check the oldest supported RuboCop version	29s
JRuby 9.4	3m 7s
Ruby 2.7	37s
Prism	32s
Ruby 3.0	1m 6s
Ruby 3.1	57s
Ruby 3.2	24s
Ruby 3.3	29s
Ruby head	24s
	8m 22s

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