panic: Fail in goroutine after TestCacheMountLockedRefs has completed

https://github.com/moby/buildkit/actions/runs/3274483652/jobs/5388072103#step:5:986

panic: Fail in goroutine after TestCacheMountLockedRefs has completed

goroutine 14 [running]:
testing.(*common).Fail(0xc000084680)
	C:/hostedtoolcache/windows/go/1.19.2/x64/src/testing/testing.go:824 +0xe5
testing.(*common).Errorf(0xc000084680, {0xb7a8e9?, 0xc000084680?}, {0xc000048290?, 0x18a465?, 0xc0000c8110?})
	C:/hostedtoolcache/windows/go/1.19.2/x64/src/testing/testing.go:941 +0x65
github.com/stretchr/testify/assert.Fail({0x1deae5c1d38, 0xc000084680}, {0xc000116000, 0x3ea}, {0x0, 0x0, 0x0})
	D:/a/buildkit/buildkit/vendor/github.com/stretchr/testify/assert/assertions.go:262 +0x384
github.com/stretchr/testify/assert.NoError({0x1deae5c1d38, 0xc000084680}, {0xcdd220, 0xc0000f84b0}, {0x0, 0x0, 0x0})
	D:/a/buildkit/buildkit/vendor/github.com/stretchr/testify/assert/assertions.go:1334 +0x105
github.com/stretchr/testify/require.NoError({0xce1790, 0xc000084680}, {0xcdd220, 0xc0000f84b0}, {0x0, 0x0, 0x0})
	D:/a/buildkit/buildkit/vendor/github.com/stretchr/testify/require/require.go:1261 +0x96
github.com/moby/buildkit/solver/llbsolver/mounts.TestCacheMountLockedRefs.func2()
	D:/a/buildkit/buildkit/solver/llbsolver/mounts/mount_test.go:291 +0x98
created by github.com/moby/buildkit/solver/llbsolver/mounts.TestCacheMountLockedRefs
	D:/a/buildkit/buildkit/solver/llbsolver/mounts/mount_test.go:289 +0x74a
FAIL	github.com/moby/buildkit/solver/llbsolver/mounts	41.347s

Seems maybe related to the timeout issue fixed by https://github.com/moby/buildkit/pull/3074 and friends? Or maybe https://github.com/moby/buildkit/issues/1685 (an old one)?

CC @crazy-max

Start in solver/llbsolver/mounts/mount_test.go at TestCacheMountLockedRefs, especially lines 289-291 shown in the panic. Reproduce the Windows failure and compare it with PR 3074 and issue 1685. Done means the test no longer reports a failure from a goroutine after the test has completed.