tools: check-imports using utf-8

PR-URL: #30220
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

tools/check-imports.py

@@ -2,6 +2,7 @@
 
 from __future__ import print_function
 import glob
+import io
 import re
 import sys
 
@@ -15,7 +16,7 @@ def do_exist(file_name, lines, imported):
 
 
 def is_valid(file_name):
-  with open(file_name) as source_file:
+  with io.open(file_name, encoding='utf-8') as source_file:
     lines = [line.strip() for line in source_file]
 
   usings, importeds, line_numbers, valid = [], [], [], True