build: test both go 1.20 and 1.21

[andaaron]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b2a9239) 91.95% compared to head (cdb4e28) 91.97%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2044      +/-   ##
==========================================
+ Coverage   91.95%   91.97%   +0.01%     
==========================================
  Files         164      164              
  Lines       27657    27657              
==========================================
+ Hits        25433    25438       +5     
+ Misses       1648     1644       -4     
+ Partials      576      575       -1     

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[andaaron]

Looks like the go.mod requires an update when used with Go 1.21.
To keep compatibility with 1.20 we would need to go mod tidy -go=1.20
But we get the error go: github.com/letsencrypt/[email protected] requires [email protected], but 1.20 is requested

Seem unlikely we can keep a single committed version of the go.mod file for both 1.20 and 1.21.

I will close this PR, and will investigate using only version 1.21 for zot release 2.0.1.