Correct word in readme #600

Job	Run time
Test isolated (ruby)	3m 25s
Test without C extension	3m 3s
Test isolated (2.3)	3m 44s
Tests: Ruby 3.1 - ubuntu	3m 5s
Tests: Ruby 2.4 - ubuntu	3m 18s
Tests: Ruby 2.7 - ubuntu	3m 18s
Tests: Ruby jruby - ubuntu	5m 9s
Tests: Ruby 3.2 - ubuntu	3m 12s
Tests: Ruby 3.3 - ubuntu	3m 7s
Tests: Ruby 2.6 - ubuntu	3m 20s
Tests: Ruby 3.0 - ubuntu	3m 5s
Tests: Ruby 3.4 - ubuntu	3m 5s
Tests: Ruby 2.3 - ubuntu	3m 24s
Tests: Ruby 2.5 - ubuntu	3m 16s
Tests: Ruby ruby - windows	5m 1s
Tests: Ruby truffleruby - ubuntu	4m 10s
	56m 42s

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