ipn/ipnlocal: TestApplySysPolicy data race

[bradfitz]

logs ...

024-05-08T04:30:26.0350698Z ==================
2024-05-08T04:30:26.0351446Z WARNING: DATA RACE
2024-05-08T04:30:26.0352092Z Write at 0x00c0002fe6c3 by goroutine 957:
2024-05-08T04:30:26.0352889Z   testing.tRunner.func1()
2024-05-08T04:30:26.0353688Z       testing/testing.go:1676 +0x8fa
2024-05-08T04:30:26.0354458Z   runtime.deferreturn()
2024-05-08T04:30:26.0355170Z       runtime/panic.go:602 +0x5d
2024-05-08T04:30:26.0355991Z   testing.(*T).Run.gowrap1()
2024-05-08T04:30:26.0356656Z       testing/testing.go:1742 +0x44
2024-05-08T04:30:26.0357112Z 
2024-05-08T04:30:26.0357428Z Previous read at 0x00c0002fe6c3 by goroutine 985:
2024-05-08T04:30:26.0358370Z   testing.(*common).logDepth()
2024-05-08T04:30:26.0359066Z       testing/testing.go:1017 +0xcd
2024-05-08T04:30:26.0359928Z   testing.(*common).log()
2024-05-08T04:30:26.0360576Z       testing/testing.go:1010 +0xa4
2024-05-08T04:30:26.0361284Z   testing.(*common).Logf()
2024-05-08T04:30:26.0362079Z       testing/testing.go:1061 +0x6a
2024-05-08T04:30:26.0362904Z   testing.(*common).Logf-fm()
2024-05-08T04:30:26.0363550Z       <autogenerated>:1 +0x69
2024-05-08T04:30:26.0364474Z   tailscale.com/ipn/ipnlocal.newTestBackend.WithPrefix.func1()
2024-05-08T04:30:26.0365408Z       tailscale.com/types/logger/logger.go:103 +0x87
2024-05-08T04:30:26.0366593Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).onHealthChange()
2024-05-08T04:30:26.0367630Z       tailscale.com/ipn/ipnlocal/local.go:675 +0x166
2024-05-08T04:30:26.0368708Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).onHealthChange-fm()
2024-05-08T04:30:26.0369574Z       <autogenerated>:1 +0x64
2024-05-08T04:30:26.0370341Z   tailscale.com/health.(*Tracker).setLocked.gowrap1()
2024-05-08T04:30:26.0371223Z       tailscale.com/health/health.go:366 +0x6e
2024-05-08T04:30:26.0371791Z 
2024-05-08T04:30:26.0372038Z Goroutine 957 (running) created at:
2024-05-08T04:30:26.0372987Z   testing.(*T).Run()
2024-05-08T04:30:26.0373667Z       testing/testing.go:1742 +0x825
2024-05-08T04:30:26.0374652Z   tailscale.com/ipn/ipnlocal.TestApplySysPolicy.func1()
2024-05-08T04:30:26.0375928Z       tailscale.com/ipn/ipnlocal/local_test.go:2123 +0x487
2024-05-08T04:30:26.0376797Z   testing.tRunner()
2024-05-08T04:30:26.0377584Z       testing/testing.go:1689 +0x21e
2024-05-08T04:30:26.0378374Z   testing.(*T).Run.gowrap1()
2024-05-08T04:30:26.0379592Z       testing/testing.go:1742 +0x44
2024-05-08T04:30:26.0380120Z 
2024-05-08T04:30:26.0380546Z Goroutine 985 (finished) created at:
2024-05-08T04:30:26.0381334Z   tailscale.com/health.(*Tracker).setLocked()
2024-05-08T04:30:26.0382195Z       tailscale.com/health/health.go:366 +0x37b
2024-05-08T04:30:26.0383266Z   tailscale.com/health.(*Tracker).selfCheckLocked()
2024-05-08T04:30:26.0384155Z       tailscale.com/health/health.go:601 +0x6d
2024-05-08T04:30:26.0385098Z   tailscale.com/health.(*Tracker).SetIPNState()
2024-05-08T04:30:26.0386081Z       tailscale.com/health/health.go:516 +0x128
2024-05-08T04:30:26.0387167Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).enterStateLockedOnEntry()
2024-05-08T04:30:26.0388686Z       tailscale.com/ipn/ipnlocal/local.go:4361 +0x457
2024-05-08T04:30:26.0390005Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).stateMachineLockedOnEntry()
2024-05-08T04:30:26.0391142Z       tailscale.com/ipn/ipnlocal/local.go:4507 +0x44
2024-05-08T04:30:26.0392228Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).stateMachine()
2024-05-08T04:30:26.0393427Z       tailscale.com/ipn/ipnlocal/local.go:4501 +0x33
2024-05-08T04:30:26.0394593Z   tailscale.com/ipn/ipnlocal.(*LocalBackend).SetControlClientStatus()
2024-05-08T04:30:26.0395891Z       tailscale.com/ipn/ipnlocal/local.go:1283 +0x265d
2024-05-08T04:30:26.0396886Z   tailscale.com/ipn/ipnlocal.TestApplySysPolicy.func1.2()
2024-05-08T04:30:26.0397973Z       tailscale.com/ipn/ipnlocal/local_test.go:2144 +0x305
2024-05-08T04:30:26.0398996Z   testing.tRunner()
2024-05-08T04:30:26.0399627Z       testing/testing.go:1689 +0x21e
2024-05-08T04:30:26.0400404Z   testing.(*T).Run.gowrap1()
2024-05-08T04:30:26.0401189Z       testing/testing.go:1742 +0x44
2024-05-08T04:30:26.0401932Z ==================
2024-05-08T04:30:26.0402657Z     testing.go:1398: race detected during execution of test
2024-05-08T04:30:26.0404134Z --- FAIL: TestApplySysPolicy/prefs_set_with_neutral_policies (0.01s)

/cc @maisem @sailorfrag