Use mode/encoding kwargs in io and unicode tests

mode argument is used to assert it works
encoding argument is used to make sure CPython uses the correct encoding
as it does not automatically use utf-8

tests/unicode/file1.py

@@ -1,4 +1,4 @@
-f = open("unicode/data/utf-8_1.txt")
+f = open("unicode/data/utf-8_1.txt", encoding="utf-8")
 l = f.readline()
 print(l)
 print(len(l))

tests/unicode/file2.py

@@ -1,7 +1,11 @@
 # test reading a given number of characters
 
 def do(mode):
-    f = open('unicode/data/utf-8_2.txt', mode)
+    if mode == 'rb':
+        enc = None
+    else:
+        enc = 'utf-8'
+    f = open('unicode/data/utf-8_2.txt', mode=mode, encoding=enc)
     print(f.read(1))
     print(f.read(1))
     print(f.read(2))