chore: use testify instead of testing in server/etcdmain

[mmorel-35]

Description

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

Related to #18972

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.82%. Comparing base (f07e2ae) to head (7e422dc).
Report is 208 commits behind head on main.

Additional details and impacted files

see 27 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19612      +/-   ##
==========================================
+ Coverage   68.77%   68.82%   +0.05%     
==========================================
  Files         421      421              
  Lines       35897    35897              
==========================================
+ Hits        24689    24707      +18     
+ Misses       9786     9764      -22     
- Partials     1422     1426       +4     

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[mmorel-35]

/assign @serathius

[jmhbnz]

LGTM - Thanks @mmorel-35

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jmhbnz, mmorel-35

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