bytes/bytearray.startswith fixes (#2696)

Author: scop

stdlib/3/builtins.pyi

@@ -387,7 +387,8 @@ class bytes(ByteString):
     def rstrip(self, chars: Optional[bytes] = ...) -> bytes: ...
     def split(self, sep: Optional[bytes] = ..., maxsplit: int = ...) -> List[bytes]: ...
     def splitlines(self, keepends: bool = ...) -> List[bytes]: ...
-    def startswith(self, prefix: Union[bytes, Tuple[bytes, ...]]) -> bool: ...
+    def startswith(self, prefix: Union[bytes, Tuple[bytes, ...]], start: Optional[int] = ...,
+                   end: Optional[int] = ...) -> bool: ...
     def strip(self, chars: Optional[bytes] = ...) -> bytes: ...
     def swapcase(self) -> bytes: ...
     def title(self) -> bytes: ...
@@ -466,7 +467,8 @@ class bytearray(MutableSequence[int], ByteString):
     def rstrip(self, chars: Optional[bytes] = ...) -> bytearray: ...
     def split(self, sep: Optional[bytes] = ..., maxsplit: int = ...) -> List[bytearray]: ...
     def splitlines(self, keepends: bool = ...) -> List[bytearray]: ...
-    def startswith(self, prefix: bytes) -> bool: ...
+    def startswith(self, prefix: Union[bytes, Tuple[bytes, ...]], start: Optional[int] = ...,
+                   end: Optional[int] = ...) -> bool: ...
     def strip(self, chars: Optional[bytes] = ...) -> bytearray: ...
     def swapcase(self) -> bytearray: ...
     def title(self) -> bytearray: ...