chore(deps): update golang docker tag to v1.21

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
golang	stage	minor	1.20 -> 1.21

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[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.10% 🎉

Comparison is base (ccce0e2) 80.01% compared to head (77c00f1) 80.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
+ Coverage   80.01%   80.11%   +0.10%     
==========================================
  Files          31       31              
  Lines        1976     1976              
==========================================
+ Hits         1581     1583       +2     
+ Misses        322      320       -2     
  Partials       73       73              

Flag	Coverage Δ
unittests	80.11% <ø> (+0.10%)	⬆️

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see 2 files with indirect coverage changes

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