bpo-43651: PEP 597: Fix EncodingWarning in some tests (GH-25145)

* test_asyncio
* test_bz2
* test_math
* test_cmath
* test_cmd_line
* test_cmd_line_script
* test_compile
* test_contextlib
* test_profile
* ctypes/test/test_find
* test_multiprocessing
* test_configparser
* test_csv
* test_dbm_dumb
* test_decimal
* test_difflib
* os.fdopen() calls io.text_encoding() to emit EncodingWarning for right place.
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 6aa4a9b..179a9ea 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -289,7 +289,7 @@ def eval_file(self, file):
         global skip_expected
         if skip_expected:
             raise unittest.SkipTest
-        with open(file) as f:
+        with open(file, encoding="utf-8") as f:
             for line in f:
                 line = line.replace('\r\n', '').replace('\n', '')
                 #print line