CI: run against Go 1.17/1.18

[abhinav]

We only support the most recent two Go minor releases.
staticcheck had to be upgraded to master for this to work.

[codecov]

Codecov Report

Merging #862 (8edff6e) into master (65e6e7f) will decrease coverage by 0.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #862      +/-   ##
==========================================
- Coverage   98.63%   98.45%   -0.19%     
==========================================
  Files          30       30              
  Lines        1100     1100              
==========================================
- Hits         1085     1083       -2     
- Misses         10       11       +1     
- Partials        5        6       +1     

Impacted Files	Coverage Δ
app.go	94.95% <0.00%> (-0.92%)	⬇️

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