x/sys/windows: test fails to build on Go 1.20 due to use of the slices package

[gopherbot]

#!watchflakes
post <- pkg == "golang.org/x/sys/windows" && log ~ `package slices is not in GOROOT`

Issue created automatically to collect these failures.

Example (log):

windows\env_windows_test.go:9:2: package slices is not in GOROOT (C:\workdir\go\src\slices)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/sys/windows" && test == ""

2024-01-23 00:04 windows-386-2016 sys@c3fa2b8b go@a95136a8 x/sys/windows [build] (log)

windows\env_windows_test.go:9:2: package slices is not in GOROOT (C:\workdir\go\src\slices)

2024-01-23 00:04 windows-amd64-2016 sys@c3fa2b8b go@a95136a8 x/sys/windows [build] (log)

windows\env_windows_test.go:9:2: package slices is not in GOROOT (C:\workdir\go\src\slices)

2024-01-23 00:04 windows-amd64-race sys@c3fa2b8b go@a95136a8 x/sys/windows [build] (log)

windows\env_windows_test.go:9:2: package slices is not in GOROOT (C:\workdir\go\src\slices)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/sys/windows" && test == ""

2024-01-23 00:04 windows-arm64-11 sys@c3fa2b8b go@a95136a8 x/sys/windows [build] (log)

windows\env_windows_test.go:9:2: package slices is not in GOROOT (C:\workdir\go\src\slices)

— watchflakes

[gopherbot]

Change https://go.dev/cl/557975 mentions this issue: windows: build env_windows_test.go only go Go 1.21 and above