datetime: mark positional-only args (#3791)

stdlib/2and3/datetime.pyi

@@ -37,7 +37,7 @@ class date:
     def __init__(self, year: int, month: int, day: int) -> None: ...
 
     @classmethod
-    def fromtimestamp(cls: Type[_S], t: float) -> _S: ...
+    def fromtimestamp(cls: Type[_S], __timestamp: float) -> _S: ...
     @classmethod
     def today(cls: Type[_S]) -> _S: ...
     @classmethod

tests/stubtest_whitelists/py38.txt

@@ -91,7 +91,6 @@ dataclasses.dataclass
 dataclasses.field
 dataclasses.make_dataclass
 dataclasses.replace
-datetime.date.fromtimestamp
 decimal.Decimal.from_float
 decimal.setcontext
 dis.stack_effect