internal/lsp/regtest: fix WithoutWorkspaceFolders option
internal/lsp/regtest: fix WithoutWorkspaceFolders option

This option was previous a no-op.

Change-Id: Id28f6802c8f5b020fb3ae71f5b941c0517ca1725
Reviewed-on: https://go-review.googlesource.com/c/tools/+/244548
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools