fix: keep import of BaseServer in server.py (#2646)

Author: PProfizi

src/ansys/dpf/core/server.py

@@ -49,7 +49,13 @@
     ServerFactory,
     GrpcMode
 )
-from ansys.dpf.core.server_types import DPF_DEFAULT_PORT, LOCALHOST, RUNNING_DOCKER, AnyServerType
+from ansys.dpf.core.server_types import (  # noqa: F401  # pylint: disable=unused-import
+    DPF_DEFAULT_PORT,
+    LOCALHOST,
+    RUNNING_DOCKER,
+    AnyServerType,
+    BaseServer,
+)
 
 
 def shutdown_global_server():