chore(deps): update docker.io/library/golang docker tag to v1.21.6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
docker.io/library/golang	stage	minor	1.20.7 -> 1.21.6

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5d39b2e) 69.45% compared to head (8dad320) 69.45%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #164   +/-   ##
=======================================
  Coverage   69.45%   69.45%           
=======================================
  Files          29       29           
  Lines        2089     2089           
=======================================
  Hits         1451     1451           
  Misses        556      556           
  Partials       82       82           

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