Pin pyfakefs to avoid broken release (#528)

* Pin pyfakefs to avoid broken release

The recent pyfakefs 4.2.0 release is raising an import error whenever
it's imported, see pytest-dev/pyfakefs#565 for more details. This commit
pins the pyfakefs version to the last known working version until there
is a new release fixing this issue.

* Ignore numba namespace in pylint

(cherry picked from commit c572b34)

constraints.txt

@@ -2,3 +2,4 @@ pylint==2.4.4
 astroid==2.3.3
 pywin32==225
 setuptools==49.6.0
+pyfakefs==4.1.0