Fix naming (#1857)

# Rationale for this change

Small copy-paste :)

# Are these changes tested?

# Are there any user-facing changes?

<!-- In the case of user-facing changes, please add the changelog label.
-->

Author: Fokko

pyiceberg/transforms.py

@@ -703,7 +703,7 @@ def hour_func(v: Any) -> int:
 
         elif isinstance(source, (TimestampNanoType, TimestamptzNanoType)):
 
-            def day_func(v: Any) -> int:
+            def hour_func(v: Any) -> int:
                 # python datetime has no nanoseconds support.
                 # nanosecond datetimes will be expressed as int as a workaround
                 return datetime.nanos_to_hours(v)