ci: build and test using 1.18 and 1.19 (drop 1.17)

[imjasonh]

k8s apimachinery now seems to require 1.18: #804

Since 1.19 came out last month, 1.17 is no longer officially supported.

This PR also removes the Go 1.18 compat e2e test, which should also let us remove some pre-1.18 compat code in a future PR. edit: just went ahead and removed the pre-1.18 code.

[codecov-commenter]

Codecov Report

Merging #812 (01d4be8) into main (3f0b618) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #812      +/-   ##
==========================================
- Coverage   51.40%   51.37%   -0.03%     
==========================================
  Files          44       44              
  Lines        3354     3354              
==========================================
- Hits         1724     1723       -1     
  Misses       1408     1408              
- Partials      222      223       +1     

Impacted Files	Coverage Δ
pkg/commands/version.go	47.36% <0.00%> (-5.27%)	⬇️

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