Re-check that the lease still exists during the renew process

[ahrtr]

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

The lease might have been revoked during renew process (right after previous check).

I will add an e2e test to reproduce the issue later.

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[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.19%. Comparing base (963a72e) to head (6d51f4b).

Files with missing lines	Patch %	Lines
server/lease/lessor.go	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
server/lease/lessor.go	88.65% <25.00%> (-0.67%)	⬇️

... and 44 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #20590      +/-   ##
==========================================
+ Coverage   67.91%   69.19%   +1.28%     
==========================================
  Files         419      420       +1     
  Lines       34762    34780      +18     
==========================================
+ Hits        23608    24066     +458     
+ Misses       9763     9318     -445     
- Partials     1391     1396       +5     

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[silentred]

make sense. lessor.Revoke is also protected by le.mu

etcd/server/lease/lessor.go

Lines 353 to 355 in 21d04d7

	le.mu.Lock()
	defer le.mu.Unlock()
	delete(le.leaseMap, l.ID)