remove support of go 1.21

[ktong]

minimum go version is go 1.22 now

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.8%. Comparing base (d34da87) to head (5920226).
Report is 41 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #457     +/-   ##
=======================================
- Coverage   82.8%   82.8%   -0.1%     
=======================================
  Files         62      62             
  Lines       2652    2651      -1     
=======================================
- Hits        2198    2197      -1     
  Misses       371     371             
  Partials      83      83             

Files	Coverage Δ
internal/convert/option.go	70.5% <100.0%> (ø)
internal/nocopy.go	100.0% <100.0%> (ø)
provider/secretmanager/secretmanager.go	89.9% <ø> (-0.1%)	⬇️