CI: Address data race in TestSchemaVersioning

[mattlord]

Description

This data race resulted from the fact that the same ctx variable/pointer is re-used in the test and because we did not wait for the goroutine to end once the previous context was cancelled before we overwrote the variable/pointer with a new context those two goroutines were racing on reads and writes of the address. So the race looked like this:

Goroutine 16633 (running) created at:
  vitess.io/vitess/go/vt/vttablet/endtoend.TestSchemaVersioning()
      /vitess/go/vt/vttablet/endtoend/vstreamer_test.go:153 +0x1455
...
==================
==================
WARNING: DATA RACE
Write at 0x00c000407020 by goroutine 16620:
  vitess.io/vitess/go/vt/vttablet/endtoend.TestSchemaVersioning()
      /vitess/go/vt/vttablet/endtoend/vstreamer_test.go:191 +0x18af
...

With those two access being:

vitess/go/vt/vttablet/endtoend/vstreamer_test.go

Lines 151 to 156 in 0d8ca1b

	select {
	case eventCh <- evs:
	case <-ctx.Done():
	return nil
	}
	return nil

vitess/go/vt/vttablet/endtoend/vstreamer_test.go

Lines 187 to 191 in 0d8ca1b

	runCases(ctx, t, cases, eventCh)
	cancel()
	log.Infof("\n\n\n=============================================== PAST EVENTS WITH TRACK VERSIONS START HERE ======================\n\n\n")
	ctx, cancel = context.WithCancel(context.Background())

This PR adds a WaitGroup to ensure that we wait for the goroutine from the previous test case — which is polling the context's done channel — to end before we overwrite the ctx variable/pointer for the next test case.

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.24%. Comparing base (a1edaee) to head (4e35f5f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15998   +/-   ##
=======================================
  Coverage   68.24%   68.24%           
=======================================
  Files        1562     1562           
  Lines      197171   197173    +2     
=======================================
+ Hits       134550   134552    +2     
  Misses      62621    62621           

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