Update dependency org.assertj:assertj-core to v3.21.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.assertj:assertj-core (source)	3.18.1 -> 3.21.0

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[codecov-commenter]

Codecov Report

Merging #255 (728aafa) into master (6f681be) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #255   +/-   ##
=========================================
  Coverage     15.78%   15.78%           
  Complexity       76       76           
=========================================
  Files            33       33           
  Lines          1311     1311           
  Branches        126      126           
=========================================
  Hits            207      207           
  Misses         1091     1091           
  Partials         13       13           

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