Non-existent relative path variables (i.e {workspaceFolderBasename}) do not squiggle even though it results in an incorrect path

[browntarik]

{workspaceFolderBasename} does not squiggle though it expands to an incorrect path

[sean-mcmanus]

This issue only seems to repro for variables that result in a relative path. I'm seeing it give a squiggle with a full path, e.g. ${workspaceFolder}.