Properly quote expected string value in lldb formatter unittests

Summary:
Sorry about breaking gdb printer tests. I must have forgotten
adapting them when merging lldb and gdb tests. Anyway, this patch uses
correct expected values in lldb tests.

Reviewers: kfunk, #kdevelop

Reviewed By: kfunk, #kdevelop

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D9929

(cherry picked from commit 06298b24)