lint: Ignore check_fileopens failure on **kwargs

This fixes a bug in the linter:

"""
Python's open(...) seems to be used to open text files without explicitly specifying encoding='utf8':
test/functional/test_framework/test_node.py:        with open(self.debug_log_path, **kwargs) as dl:
"""

Author: MarcoFalke

test/lint/lint-python-utf8-encoding.py

@@ -28,7 +28,7 @@ def check_fileopens():
         if e.returncode > 1:
             raise e
 
-    filtered_fileopens = [fileopen for fileopen in fileopens if not re.search(r"encoding=.(ascii|utf8|utf-8).|open\([^,]*, ['\"][^'\"]*b[^'\"]*['\"]", fileopen)]
+    filtered_fileopens = [fileopen for fileopen in fileopens if not re.search(r"encoding=.(ascii|utf8|utf-8).|open\([^,]*, (\*\*kwargs|['\"][^'\"]*b[^'\"]*['\"])", fileopen)]
 
     return filtered_fileopens