build(deps): bump Externals/imgui from `259560a` to `d6ea56d`

Created by: dependabot[bot]

Bumps Externals/imgui from 259560a to d6ea56d.

Commits

• d6ea56d Tables: amend f799a29 with a better solution + fix potential overflow (#6140)
• ea39841 Examples: (Again, but better) made SDL+GL and GLFW+GL examples build with Ems...
• f43c6ea Revert most of "Examples: refactor all examples with a MainLoopStep() functio...
• f799a29 Tables: Solved an ID conflict issue with multiple-instances of a same table. ...
• c75410e Debug: fix display order of InputText's data CurLenA/CurLenW (#6143)
• a085581 Backends: GLFW: added ImGui_ImplGlfw_SetCallbacksChainForAllWindows(). (#6142)
• 265b882 Backends: Fixed pragma warning with old GCC.
• d0b1aaa Backends: GLFW: Registering custom low-level mouse wheel handler to get more ...
• 6584de4 Backends: SDL: Avoid calling SDL_SetCursor() when cursor has not changed. (#6...
• 46efed8 CI: Fix Emscripten build.
• Additional commits viewable in compare view

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