fix: join on, how args are now positional (#2140)

Author: TrevorBergeron

bigframes/dataframe.py

@@ -3721,7 +3721,6 @@ def _validate_left_right_on(
     def join(
         self,
         other: Union[DataFrame, bigframes.series.Series],
-        *,
         on: Optional[str] = None,
         how: str = "left",
         lsuffix: str = "",

third_party/bigframes_vendored/pandas/core/frame.py

@@ -4601,9 +4601,8 @@ def map(self, func, na_action: Optional[str] = None) -> DataFrame:
     def join(
         self,
         other,
-        *,
         on: Optional[str] = None,
-        how: str,
+        how: str = "left",
         lsuffix: str = "",
         rsuffix: str = "",
     ) -> DataFrame: