qedit/tests: Constify some character strings

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://newtestbot.winehq.org/JobDetails.pl?Key=3869

Your paranoid android.


=== w2008s64 (32 bit mediadet) ===
mediadet.c:149: Test failed: CoCreateInstance failed: 80040154
mediadet: unhandled exception c0000005 at 0040185A

=== w2008s64 (64 bit mediadet) ===
mediadet.c:149: Test failed: CoCreateInstance failed: 80040154
mediadet: unhandled exception c0000005 at 00000000004017C3