tests: add some b-prefixes on local script in test-histedit-arguments

# skip-blame its just more b prefixes and a file in binary mode

Differential Revision: https://phab.mercurial-scm.org/D2247

tests/test-histedit-arguments.t

@@ -280,9 +280,9 b' Test that trimming description using mul'
 --------------------------------------------------------------------
 
   $ $PYTHON <<EOF
-  > fp = open('logfile', 'w')
-  > fp.write('12345678901234567890123456789012345678901234567890' +
-  >          '12345') # there are 5 more columns for 80 columns
+  > fp = open('logfile', 'wb')
+  > fp.write(b'12345678901234567890123456789012345678901234567890' +
+  >          b'12345') # there are 5 more columns for 80 columns
   > 
   > # 2 x 4 = 8 columns, but 3 x 4 = 12 bytes
   > fp.write(u'\u3042\u3044\u3046\u3048'.encode('utf-8'))