x/tools/gopls: TryBot flake in TestDeleteFiles/delete_then_close/default

[findleyr]

The following flake occured on https://go.dev/cl/422135:

https://storage.googleapis.com/go-build-log/a34a97d8/freebsd-amd64-12_3_7f502470.log

greplogs does not turn up any recent flakes on the builders, but this one flake suggests that there may be a race to logging (which makes sense, as logs might be asynchronous).