migrate CharSequenceNotToContainOrAtMostExpectationsSpec to kotlin-test

[robstoll]

Platform (all, jvm, js): all
Extension (none, kotlin 1.3): none

Code related feature

We want to move away from Spek as test-runner as we consider this project dead and it makes more and more problems in conjunction with intellij and gradle. Hence, we migrate the tests in atrium-specs to kotlin-test.

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