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 (8da854d) to head (5dc69b7).
Report is 18 commits behind head on main.

❗ Current head 5dc69b7 differs from pull request most recent head eea3dd6

Please upload reports for the commit eea3dd6 to get more accurate results.

Additional details and impacted files

see 51 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19613      +/-   ##
==========================================
+ Coverage   66.02%   68.78%   +2.75%     
==========================================
  Files         424      421       -3     
  Lines       35862    35857       -5     
==========================================
+ Hits        23679    24665     +986     
+ Misses      10774     9762    -1012     
- Partials     1409     1430      +21     

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[mmorel-35]

/assign @fuweid

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mmorel-35
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[k8s-ci-robot]

@mmorel-35: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-etcd-grpcproxy-integration-arm64	eea3dd6	link	true	/test pull-etcd-grpcproxy-integration-arm64
pull-etcd-coverage-report	eea3dd6	link	true	/test pull-etcd-coverage-report

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