#4591 do not treat warnings as error in teamcity

[tlamy]

As suggested by Jetbrains in https://youtrack.jetbrains.com/issue/WI-57958 , just write warnings to stdout in the teamcity logger. This fixes #4591.
Should I create a PR for 8.5.x, as it may be worth having it there also?

[codecov]

Codecov Report

Merging #4623 (73be161) into master (6eb1bc9) will increase coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #4623      +/-   ##
============================================
+ Coverage     83.30%   83.34%   +0.03%     
  Complexity     4525     4525              
============================================
  Files           292      292              
  Lines         11934    11929       -5     
============================================
  Hits           9942     9942              
+ Misses         1992     1987       -5     

Impacted Files	Coverage Δ	Complexity Δ
src/Util/Log/TeamCity.php	59.28% <0.00%> (+2.04%)	56.00 <0.00> (ø)

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[sebastianbergmann]

Cherry-picked into 8.5 and merged to 9.5 and master from there. Thanks!