Fix a log formatting bug in the e2e downgrade tests

[henrybear327]

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

The log message was of the following format before fixing

cluster_downgrade_test.go:163: Elect members for operations
        %!(EXTRA zapcore.Field={members 1 0  [2 1]})

After

 cluster_downgrade_test.go:163: Elect members for operations zapcore.Field{Key:"members", Type:0x1, Integer:0, String:"", Interface:zap.ints{1}}

[henrybear327]

/retest

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.85%. Comparing base (9de211d) to head (89dd13f).
Report is 2 commits behind head on main.

Additional details and impacted files

see 29 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19367      +/-   ##
==========================================
- Coverage   68.98%   68.85%   -0.14%     
==========================================
  Files         420      420              
  Lines       35739    35739              
==========================================
- Hits        24656    24609      -47     
- Misses       9660     9702      +42     
- Partials     1423     1428       +5     

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[henrybear327]

/retest

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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