Do not show an icon in checks report when the coverage did not change

[uhafner]

Fixes #662

[codecov]

Codecov Report

Merging #665 (be43693) into master (e486bea) will decrease coverage by 0.01%.
The diff coverage is 75.00%.

@@             Coverage Diff              @@
##             master     #665      +/-   ##
============================================
- Coverage     73.55%   73.55%   -0.01%     
  Complexity     1663     1663              
============================================
  Files           129      129              
  Lines          6240     6236       -4     
  Branches        668      667       -1     
============================================
- Hits           4590     4587       -3     
+ Misses         1431     1430       -1     
  Partials        219      219              

Impacted Files	Coverage Δ
...s/plugins/coverage/metrics/steps/PathResolver.java	65.47% <ø> (ø)
...overage/metrics/steps/CoverageChecksPublisher.java	93.10% <75.00%> (+0.30%)	⬆️

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