fix pathlib tests to not use binary mode

Since errors shouldn't be used with binary modes. Maybe should just
delete?

Author: hauntsaninja

test-data/unit/pythoneval.test

@@ -313,13 +313,13 @@ _program.py:7: note: Revealed type is 'typing.IO[Any]'
 [case testPathOpenReturnTypeInferenceSpecialCases]
 from pathlib import Path
 p = Path("x")
-reveal_type(p.open(mode='rb', errors='replace'))
-reveal_type(p.open(errors='replace', mode='rb'))
-mode = 'rb'
+reveal_type(p.open(mode='r', errors='replace'))
+reveal_type(p.open(errors='replace', mode='r'))
+mode = 'r'
 reveal_type(p.open(mode=mode, errors='replace'))
 [out]
-_program.py:3: note: Revealed type is 'typing.BinaryIO'
-_program.py:4: note: Revealed type is 'typing.BinaryIO'
+_program.py:3: note: Revealed type is 'io.TextIOWrapper'
+_program.py:4: note: Revealed type is 'io.TextIOWrapper'
 _program.py:6: note: Revealed type is 'typing.IO[Any]'
 
 [case testGenericPatterns]