Add CI on Go 1.18

[at-wat]

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[codecov]

Codecov Report

Merging #204 (66b028b) into master (07acc1b) will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #204      +/-   ##
==========================================
+ Coverage   92.03%   92.19%   +0.15%     
==========================================
  Files          34       34              
  Lines        1896     1896              
==========================================
+ Hits         1745     1748       +3     
+ Misses        129      127       -2     
+ Partials       22       21       -1     

Impacted Files	Coverage Δ
serve.go	94.44% <0.00%> (+2.08%)	⬆️

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