Make detekt a bit less noisy when mixing java and kotlin files

[BraisGabin]

Only print not handled files in debug mode.

Fix #3788

[codecov]

Codecov Report

Merging #4231 (5ff70e1) into main (1f1e888) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main    #4231   +/-   ##
=========================================
  Coverage     84.32%   84.32%           
  Complexity     3240     3240           
=========================================
  Files           468      468           
  Lines         10167    10167           
  Branches       1778     1778           
=========================================
  Hits           8573     8573           
  Misses          658      658           
  Partials        936      936           

Impacted Files	Coverage Δ
...io/gitlab/arturbosch/detekt/core/KtTreeCompiler.kt	78.78% <100.00%> (ø)

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