CI: add Ruby 3.3 to the test matrix #5

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Run time

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Job	Run time
Test (Ruby 2.3)	31s
Test (Ruby 2.4)	1m 2s
Test (Ruby 2.5)	27s
Test (Ruby 2.6)	31s
Test (Ruby 2.7)	32s
Test (Ruby 3.0)	15s
Test (Ruby 3.1)	26s
Test (Ruby 3.2)	18s
Test (Ruby 3.3)	19s
Test (Ruby jruby)	42s
Test (Ruby truffleruby)	32s
Test (Ruby 2.0)	16s
Test (Ruby 2.1)	24s
Test (Ruby 2.2)	31s
	6m 46s