BUG: Fix dt64[non_nano] + offset rounding

Author: Aniketsy

pandas/core/arrays/datetimes.py

@@ -815,6 +815,12 @@ def _add_offset(self, offset: BaseOffset) -> Self:
                     stacklevel=find_stack_level(),
                 )
             res_values = self.astype("O") + offset
+            res_values = [
+                Timestamp(x)
+                if isinstance(x, datetime) and not isinstance(x, Timestamp)
+                else x
+                for x in res_values
+            ]
             result = type(self)._from_sequence(res_values, dtype=self.dtype)
 
         else: