Use Go 1.21 built-in min function

[cppcoffee]

This pull request proposes an update to the Go version, elevating it from 1.20 to 1.21.

This change is dependent on pion/.goassets#233

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.78%. Comparing base (ff2807d) to head (578fc25).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #355      +/-   ##
==========================================
+ Coverage   78.71%   78.78%   +0.07%     
==========================================
  Files          82       82              
  Lines        5169     5139      -30     
==========================================
- Hits         4069     4049      -20     
+ Misses        927      920       -7     
+ Partials      173      170       -3     

Flag	Coverage Δ
go	78.67% <100.00%> (-0.05%)	⬇️
wasm	76.27% <100.00%> (+0.17%)	⬆️

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[JoTurk]

Hello I changed this PR to a draft until we upgrade to go 1.21. We can't right now because it will force many users to stuck with older version of pion!