Remove duplicated <-s.ReadyNotify()

[ahrtr]

Follow up to #19041

It was a mistake that I made when debugging the codecov/patch failure in #19041. Sorry. Also refer to #19046 (comment)

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[serathius]

Should we add a test for shutdown during initialization?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.84%. Comparing base (026bbec) to head (16ccfc9).
Report is 2 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
server/embed/serve.go	57.19% <ø> (-0.16%)	⬇️

... and 23 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19057      +/-   ##
==========================================
+ Coverage   68.79%   68.84%   +0.04%     
==========================================
  Files         420      420              
  Lines       35627    35626       -1     
==========================================
+ Hits        24509    24525      +16     
+ Misses       9688     9680       -8     
+ Partials     1430     1421       -9     

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[ahrtr]

/retest

[ahrtr]

Should we add a test for shutdown during initialization?

It's good to have, but hard to test. The problem is that etcd doesn't wait for the following goroutine to complete or exit when it's stopping. So from product functionality perspective, we don't see any issue. This PR (and previous one) just avoids some unnecessary operations when the server is stopping.

etcd/server/embed/etcd.go

Lines 777 to 779 in 026bbec

	go func(s *serveCtx) {
	e.errHandler(s.serve(e.Server, &e.cfg.ClientTLSInfo, mux, e.errHandler, e.grpcGatewayDial(splitHTTP), splitHTTP, gopts...))
	}(sctx)

Even the goroutine leakage detection can't detect it either, because a golang program execution does not wait for the invoked function to complete.

etcd/client/pkg/testutil/leak.go

Lines 101 to 109 in 026bbec

	func RegisterLeakDetection(t TB) {
	if err := CheckAfterTest(10 * time.Millisecond); err != nil {
	t.Skip("Found leaked goroutined BEFORE test", err)
	return
	}
	t.Cleanup(func() {
	afterTest(t)
	})
	}

[ahrtr]

An related but different case: I recall that user applications might run into a deadlock in embeded use case if etcd is being stopped during bootstrap. Raised #19058