Fixes #1045 - Correctly resolve mapped drive on Windows

fs.realpath.native in NodeJS uses the Win32 API function GetFinalPathNameByHandle() on Windows hosts,
therefore a given path must follow the guidelines for Win32 API file functions.
Drive letters on Windows need to end on a backslash according to the Win32 File Naming Conventions (https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file)
Omitting the backslash results in Windows treating the remaining path components as a relative path starting from the current directory on the specified disk
https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#fully-qualified-vs-relative-paths

src/git/gitService.ts

@@ -3231,7 +3231,7 @@ export class GitService implements Disposable {
 
 						try {
 							const networkPath = await new Promise<string | undefined>(resolve =>
-								fs.realpath.native(`${letter}:`, { encoding: 'utf8' }, (err, resolvedPath) =>
+								fs.realpath.native(`${letter}:\\`, { encoding: 'utf8' }, (err, resolvedPath) =>
 									resolve(err != null ? undefined : resolvedPath),
 								),
 							);