Update eclipse-mosquitto Docker tag to v2.0.21

[renovate]

This PR contains the following updates:

Package	Update	Change
eclipse-mosquitto	patch	2.0.20 -> 2.0.21

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Configuration

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.25%. Comparing base (9f06b1c) to head (c72db43).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
+ Coverage   91.06%   91.25%   +0.19%     
==========================================
  Files          38       38              
  Lines        2092     2092              
==========================================
+ Hits         1905     1909       +4     
+ Misses        166      163       -3     
+ Partials       21       20       -1     

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