Bump MyGUI

EDIT: mygui dev released 3.4.2 which includes the fix for building with gcc 13 . see https://github.com/MyGUI/mygui/releases/tag/MyGUI3.4.2 for details

openmw trunk 61691da5

when building with gcc 13.1 builds fails . Investigating revealed that this is caused by mygui headers. mygui 3.4.1 is not compatible with gcc 13.1 .

See https://github.com/MyGUI/mygui/pull/249 and https://github.com/MyGUI/mygui/issues/250 . Applying the fix to mygui 3.4.1 locally does solve the issue.

Building using the mygui version fetched by openmw instead of the system provided library gave the same error.

I looked at openmw/extern/CMakeLists.txt and found

 # master on 13 Mar 2021
    include(FetchContent)
    FetchContent_Declare(mygui
        URL https://github.com/MyGUI/mygui/archive/59c1388b942721887d18743ada15f1906ff11a1f.zip
        URL_HASH SHA512=56b112b261fdc4c9b782de8ef8a9d239af3a75b8cfaa617daecc77c38ecd6521624cf5c17e6ac839b0870be5c31608d4f2a1574165d9d049f14f9e6ae03a8f98
        SOURCE_DIR fetched/mygui
    )
    FetchContent_MakeAvailableExcludeFromAll(mygui)

The mygui version used by openmw 0.49 & 0.48 needs to be updated.