Migrate WALVersion to fix unexported-return of walVersion

[aladesawe]

This fixes WALVersion for issue
Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @aladesawe. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[aladesawe]

Pulled from PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.84%. Comparing base (4abcda4) to head (47a0e10).

Additional details and impacted files

Files with missing lines	Coverage Δ
server/storage/schema/schema.go	100.00% <ø> (ø)
server/storage/wal/version.go	51.53% <100.00%> (ø)

... and 26 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19350      +/-   ##
==========================================
- Coverage   68.85%   68.84%   -0.02%     
==========================================
  Files         420      420              
  Lines       35716    35716              
==========================================
- Hits        24594    24589       -5     
- Misses       9694     9696       +2     
- Partials     1428     1431       +3     

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[ivanvc]

/ok-to-test

[ahrtr]

Let's just remove it and use wal.Version directly.