[Robustness Test] Enable Antithesis nightly workflow

[henrybear327]

We disabled the nightly run due discussions in #19750. With this PR, we will enable it.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

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[henrybear327]

PR will be rebased as soon as #19750 is merged, so the diff will make sense.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.79%. Comparing base (be71a86) to head (78cfee5).

Additional details and impacted files

see 15 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19761      +/-   ##
==========================================
- Coverage   68.82%   68.79%   -0.03%     
==========================================
  Files         421      421              
  Lines       35857    35857              
==========================================
- Hits        24678    24669       -9     
- Misses       9756     9759       +3     
- Partials     1423     1429       +6     

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[serathius]

Let's wait until Anthithesis test starts doing exploration.