bug fix - detect console mode using bpy.app.background

[Andrej730]

Resolves errors like below on register() if blender is currently in background mode:

Exception in module register(): \Blender\4.2\extensions\blender_org\screencast_keys\__init__.py
Traceback (most recent call last):
  File "\Blender\4.2\scripts\modules\addon_utils.py", line 482, in enable
    mod.register()
  File "\Blender\4.2\extensions\blender_org\screencast_keys\__init__.py", line 135, in register
    gpu_utils.shader.ShaderManager.register_shaders()
  File "\Blender\4.2\extensions\blender_org\screencast_keys\gpu_utils\shader.py", line 52, in register_shaders
    gpu.platform.backend_type_get() != 'OPENGL':

[nutti]

@Andrej730 Thank you!