Handle dynamic mocks specially for null-object doubles #816

Job	Run time
Ruby 2.7 (Windows)	3m 41s
Rubocop	27s
Ruby 2.6 (Windows)	3m 41s
Legacy Ruby Builds (2.1.9)	1m 16s
Ruby 2.5 (Windows)	2m 40s
Ruby 3.3	2m 21s
Legacy Ruby Builds (2.0)	1m 13s
Ruby 2.4 (Windows)	2m 39s
Ruby 3.2	2m 18s
Legacy Ruby Builds (1.9.3)	1m 12s
Ruby 2.3 (Windows)	2m 28s
Ruby 3.1	2m 17s
Ruby 3.0	2m 31s
Legacy Ruby Builds (1.9.2)	1m 44s
Ruby 2.2 (Windows)	2m 47s
Ruby 2.7	3m 51s
Legacy Ruby Builds (1.8.7)	1m 9s
Ruby 2.6	3m 43s
Legacy Ruby Builds (REE)	1m 22s
Ruby 2.5	3m 44s
Legacy Ruby Builds (JRuby 1.7)	4m 10s
Ruby 2.4	2m 21s
Legacy Ruby Builds (JRuby 1.7 1.8 mode)	3m 31s
Ruby 2.3	2m 24s
Legacy Ruby Builds (JRuby 9.1.17.0)	4m 47s
Ruby 2.2	2m 49s
Ruby ruby-head	27s
Ruby jruby-9.2.13.0	7m 9s
Ruby 2.7 with diff-lcs 1.3	3m 40s
Ruby 2.7 with diff-lcs 1.4.3	3m 41s
	1h 22m 3s

Provide feedback