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

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
golang	final	minor	1.20-alpine -> 1.21-alpine

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[codecov-commenter]

Codecov Report

Merging #161 (dac7e6b) into master (94cb798) will not change coverage.
The diff coverage is n/a.

❗ Current head dac7e6b differs from pull request most recent head a29d717. Consider uploading reports for the commit a29d717 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #161   +/-   ##
=======================================
  Coverage   79.08%   79.08%           
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  Files          17       17           
  Lines        2271     2271           
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  Hits         1796     1796           
  Misses        287      287           
  Partials      188      188