Mark the TestListener interface as deprecated

[rpkamp]

No description provided.

[codecov]

Codecov Report

Merging #3382 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3382   +/-   ##
=========================================
  Coverage     82.95%   82.95%           
  Complexity     3569     3569           
=========================================
  Files           143      143           
  Lines          9499     9499           
=========================================
  Hits           7880     7880           
  Misses         1619     1619

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[sebastianbergmann]

Thank you for your contribution. I appreciate the time you invested in preparing this pull request. However, I have decided not to merge it.

This will be done in #3388.