Trim any trailing separator from the original root in diskRoot

Since $originalRoot can be an OS path (with local disks without root_override) or a remote path/key (e.g. with S3 or FTP), we can't assume either separator while trimming. Trimming only '/' missed a trailing '\' on a Windows local root, so e.g. 'C:\app\uploads\' became 'C:\app\uploads\/tenant1'.

(The appended '/' stays as is -- it's accepted on Windows and it's the only correct separator for remote disks.)

Note that in practice, this wasn't an issue that could break anything. But assuming '/' in the rtrim code was incorrect.

src/Bootstrappers/FilesystemTenancyBootstrapper.php

@@ -164,7 +164,7 @@ class FilesystemTenancyBootstrapper implements TenancyBootstrapper
             // This is executed if the disk is in tenancy.filesystem.disks but does NOT have a root_override
             // This behavior is used for disks like S3.
             $newRoot = $originalRoot
-                ? rtrim($originalRoot, '/') . '/' . $suffix
+                ? rtrim($originalRoot, '/\\') . '/' . $suffix
                 : $suffix;
         }