Do not pollute source directory by tests #7084

Job	Run time
Rubygems on macOS (3.3)	1m 46s
Rubygems on macOS (3.4)	4m 42s
Rubygems on Ubuntu (truffleruby)	3m 39s
Rubygems on Ubuntu (3.3)	2m 24s
Rubygems on Windows (3.3)	4m 19s
Rubygems on macOS (3.2)	1m 53s
Rubygems on Ubuntu (3.4)	4m 29s
Rubygems on Windows (3.4)	4m 16s
Rubygems on Ubuntu (3.2)	2m 9s
Rubygems on Ubuntu (jruby)	7m 5s
Rubygems on Windows (3.2)	3m 59s
All rubygems jobs pass	5s
	40m 46s

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