golangci-lint: Disable forcetypeassert for tests

[mstoykov]

What?

Disable forcetypeassert on tests.

Why?

It seems most core developers agree this isn't really a good linter for tests and makes a lot of them more complicated or longer.

see #3701 (comment)

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.24%. Comparing base (d7b37b3) to head (1e1f94b).

❗ Current head 1e1f94b differs from pull request most recent head 64e4aac. Consider uploading reports for the commit 64e4aac to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3704      +/-   ##
==========================================
+ Coverage   73.22%   73.24%   +0.01%     
==========================================
  Files         276      276              
  Lines       20384    20384              
==========================================
+ Hits        14926    14930       +4     
+ Misses       4502     4498       -4     
  Partials      956      956              

Flag	Coverage Δ
ubuntu	73.24% <ø> (+0.01%)	⬆️

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The base branch was changed.