_utils.py: fix pylint and mypy

Author: abderrahim

setup.cfg

@@ -28,7 +28,7 @@ warn_no_return = True
 
 # Ignore missing stubs for third-party packages.
 # In future, these should be re-enabled if/when stubs for them become available.
-[mypy-copyreg,grpc,pluginbase,psutil,pyroaring,ruamel,multiprocessing.forkserver]
+[mypy-copyreg,grpc,pluginbase,psutil,pyroaring,ruamel,multiprocessing.forkserver,cython.*]
 ignore_missing_imports=True
 
 # Ignore issues with generated files and vendored code

src/buildstream/_utils.py

@@ -22,9 +22,9 @@
 This module contains utilities that have been optimized in Cython
 """
 
-import cython
-from cython.cimports.cpython.pystate import PyThreadState_SetAsyncExc
-from cython.cimports.cpython.ref import PyObject
+import cython # pylint: disable=import-error
+from cython.cimports.cpython.pystate import PyThreadState_SetAsyncExc # pylint: disable=import-error
+from cython.cimports.cpython.ref import PyObject # pylint: disable=import-error
 from ._signals import TerminateException