devtools: Fix setPathHelper bug in checking for valid workspaces.
devtools: Fix setPathHelper bug in checking for valid workspaces.

The current code has a bug where the infrastructure project shows
up in "v23 go env" and basically all "v23 go" commands, even
though the infrastructure project has no go workspace.

This CL fixes that bug.

Change-Id: I632fdbdf0e4aca8f8b7ea7187e91900ec2165b40

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools