Make ruby-core job use a non moving target #5454

Job	Run time
Rubygems on Ubuntu (3.1)	1m 59s
Rubygems on Ubuntu (3.2)	1m 52s
Rubygems on Ubuntu (3.3)	2m 4s
Rubygems on Ubuntu (3.4)	3m 57s
Rubygems on macOS (3.1)	1m 36s
Rubygems on macOS (3.2)	1m 33s
Rubygems on macOS (3.3)	2m 1s
Rubygems on macOS (3.4)	3m 15s
Rubygems on Windows (3.1)	4m 5s
Rubygems on Windows (3.2)	3m 33s
Rubygems on Windows (3.3)	4m 38s
Rubygems on Windows (3.4)	4m 16s
Rubygems on Ubuntu (jruby)	6m 55s
Rubygems on Ubuntu (truffleruby)	3m 38s
	45m 22s

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