fix: Change the mapdl_inprocess graphics backend (#3915)

* Fix mapdl inprocess backend

`mapdl_inprocess` should use `None`for graphics
backend. This will have to be revisited with some
automated tests when 2025R2 is released.

* chore: adding changelog file 3915.fixed.md [dependabot-skip]

* chore: adding changelog file 3915.fixed.md [dependabot-skip]

* remove unused import

---------

Co-authored-by: Mohamed Koubaa <[email protected]>
Co-authored-by: pyansys-ci-bot <[email protected]>

Author: 3 people

doc/changelog.d/3915.fixed.md

@@ -0,0 +1 @@
+fix: Change the mapdl_inprocess graphics backend

src/ansys/mapdl/core/mapdl_inprocess.py

@@ -23,7 +23,6 @@
 from typing import Protocol
 
 from ansys.mapdl.core.mapdl import MapdlBase
-from ansys.mapdl.core.plotting import GraphicsBackend
 
 
 class _Backend(Protocol):
@@ -46,7 +45,7 @@ class MapdlInProcess(MapdlBase):
     def __init__(self, in_process_backend: _Backend):
         super().__init__(
             loglevel="WARNING",
-            graphics_backend=GraphicsBackend.MAPDL,
+            graphics_backend=None,
             log_apdl=None,
             print_com=False,
         )