[TypeSpec Validation] Rule NpmPrefix fails on Windows with lower-case drive letter

[mikeharder]

C:\>cd /d c:\git\specs

c:\git\specs>npm ci

c:\git\specs>npx tsv specification\contosowidgetmanager\Contoso.WidgetManager
Running TypeSpecValidation on folder: specification/contosowidgetmanager/Contoso.WidgetManager

Executing rule: NpmPrefix
run command:npm prefix
Expected npm prefix: C:\git\specs
Actual npm prefix: c:\git\specs
Rule NpmPrefix failed

We will probably need/want to do case-insensitive path compare on Windows, since Node APIs are inconsitent:

nodejs/node#6624