fix: downgrade minimum Go version

[ldez]

Since go1.21, the Go version used inside the go.mod is the minimum Go version and it's a hard requirement.

golangci-lint must support compilation with go1.22 and go1.23.

[ldez]

friendly ping @timonwong

[codecov]

Codecov Report

Attention: Patch coverage is 68.42105% with 6 lines in your changes missing coverage. Please review.

Project coverage is 97.79%. Comparing base (4e02d5e) to head (590af02).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/checkers/types.go	60.00%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   98.72%   97.79%   -0.94%     
==========================================
  Files          13       14       +1     
  Lines         470      589     +119     
==========================================
+ Hits          464      576     +112     
- Misses          3       10       +7     
  Partials        3        3              

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[timonwong]

@ldez I think I need to create build tags to handle reflect pacakge change since #89, just downgrading go.mod version may not work

[timonwong]

I'm working on it

[ldez]

@timonwong I created a PR to handle aliases with the official approach: #93