chore: use testify instead of testing in server/etcdserver

[mmorel-35]

Description

This uses testify instead of testing for t.Fatal or t.Error calls in server/etcdserver package

Related to #18972

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.78%. Comparing base (d6416b8) to head (5dc69b7).

Additional details and impacted files

see 40 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19613      +/-   ##
==========================================
+ Coverage   65.98%   68.78%   +2.80%     
==========================================
  Files         421      421              
  Lines       35857    35857              
==========================================
+ Hits        23659    24665    +1006     
+ Misses      10791     9762    -1029     
- Partials     1407     1430      +23     

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[mmorel-35]

/assign @fuweid

[k8s-ci-robot]

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