net/http: TestServerShutdown_h2 failures

[gopherbot]

#!watchflakes
post <- pkg == "net/http" && test == "TestServerShutdown_h2"

Issue created automatically to collect these failures.

Example (log):

--- FAIL: TestServerShutdown_h2 (0.05s)
    serve_test.go:5677: second request should fail. server should be shut down
panic: test timed out after 3m0s

goroutine 10885 [running]:
panic({0x84a320, 0xc0011aa020})
	/workdir/go/src/runtime/panic.go:987 +0x3bb fp=0xc000b5cf98 sp=0xc000b5ced8 pc=0x43751b
testing.(*M).startAlarm.func1()
	/workdir/go/src/testing/testing.go:2107 +0x8e fp=0xc000b5cfe0 sp=0xc000b5cf98 pc=0x5001ee
runtime.goexit()
	/workdir/go/src/runtime/asm_amd64.s:1594 +0x1 fp=0xc000b5cfe8 sp=0xc000b5cfe0 pc=0x46c561
created by time.goFunc
	/workdir/go/src/time/sleep.go:176 +0x32

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "net/http" && test == "TestServerShutdown_h2"

2022-09-30 03:08 linux-amd64-alpine go@9faf6b79 net/http.TestServerShutdown_h2 (log)

--- FAIL: TestServerShutdown_h2 (0.05s)
    serve_test.go:5677: second request should fail. server should be shut down
panic: test timed out after 3m0s

goroutine 10885 [running]:
panic({0x84a320, 0xc0011aa020})
	/workdir/go/src/runtime/panic.go:987 +0x3bb fp=0xc000b5cf98 sp=0xc000b5ced8 pc=0x43751b
testing.(*M).startAlarm.func1()
	/workdir/go/src/testing/testing.go:2107 +0x8e fp=0xc000b5cfe0 sp=0xc000b5cf98 pc=0x5001ee
runtime.goexit()
	/workdir/go/src/runtime/asm_amd64.s:1594 +0x1 fp=0xc000b5cfe8 sp=0xc000b5cfe0 pc=0x46c561
created by time.goFunc
	/workdir/go/src/time/sleep.go:176 +0x32

— watchflakes

[bcmills]

Compare #38305, #54758 (comment).

[neild]

Duplicate of #56421