add codecov.yml, fix error

[matyhtf]

No description provided.

[codecov]

Codecov Report

Merging #4232 (4adea9a) into master (af1722e) will increase coverage by 0.69%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4232      +/-   ##
==========================================
+ Coverage   50.11%   50.81%   +0.69%     
==========================================
  Files          71       70       -1     
  Lines       14296    14098     -198     
==========================================
- Hits         7165     7164       -1     
+ Misses       7131     6934     -197     

Impacted Files	Coverage Δ
src/server/port.cc	50.00% <0.00%> (-0.28%)	⬇️
src/core/error.cc
src/protocol/base.cc	65.13% <0.00%> (+1.97%)	⬆️

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