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

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mmorel-35
Once this PR has been reviewed and has the lgtm label, please assign fuweid for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.90%. Comparing base (f07e2ae) to head (478bf0d).

Additional details and impacted files

see 20 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19613      +/-   ##
==========================================
+ Coverage   68.77%   68.90%   +0.12%     
==========================================
  Files         421      421              
  Lines       35897    35897              
==========================================
+ Hits        24689    24735      +46     
+ Misses       9786     9742      -44     
+ Partials     1422     1420       -2     

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f07e2ae...478bf0d. Read the comment docs.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.