Fix mysql specs and add codecov #60

Job	Run time
RSpec PostgreSQL 14, Ruby 3.1, Rails 6_1	2m 43s
RSpec PostgreSQL 14, Ruby 3.1, Rails 7_0	2m 38s
RSpec PostgreSQL 14, Ruby 3.1, Rails 7_1	2m 43s
RSpec PostgreSQL 14, Ruby 3.1, Rails 7_2	2m 41s
RSpec PostgreSQL 14, Ruby 3.2, Rails 6_1	2m 39s
RSpec PostgreSQL 14, Ruby 3.2, Rails 7_0	2m 51s
RSpec PostgreSQL 14, Ruby 3.2, Rails 7_1	2m 41s
RSpec PostgreSQL 14, Ruby 3.2, Rails 7_2	2m 37s
RSpec PostgreSQL 14, Ruby 3.3, Rails 6_1	2m 43s
RSpec PostgreSQL 14, Ruby 3.3, Rails 7_0	2m 42s
RSpec PostgreSQL 14, Ruby 3.3, Rails 7_1	2m 40s
RSpec PostgreSQL 14, Ruby 3.3, Rails 7_2	2m 42s
RSpec PostgreSQL 14, Ruby jruby, Rails 6_1	2m 17s
RSpec PostgreSQL 14, Ruby jruby, Rails 7_0	2m 21s
	36m 58s

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