Update CI environment lockfiles (#4137)

* Updated environment lockfiles

* Fix add_weekday. (#4169)

Co-authored-by: Lockfile bot <noreply@github.com>
Co-authored-by: Martin Yeo <40734014+trexfeathers@users.noreply.github.com>

lib/iris/coord_categorisation.py

@@ -93,7 +93,7 @@ def vectorised_fn(*args):
 # Private "helper" function
 def _pt_date(coord, time):
     """
-    Return the date of a time-coordinate point.
+    Return the datetime of a time-coordinate point.
 
     Args:
 
@@ -103,14 +103,12 @@ def _pt_date(coord, time):
         value of a coordinate point
 
     Returns:
-        datetime.date
+        cftime.datetime
+
     """
     # NOTE: All of the currently defined categorisation functions are
     # calendar operations on Time coordinates.
-    #  - All these currently depend on Unit::num2date, which is deprecated (!!)
-    #  - We will want to do better, when we sort out our own Calendars.
-    #  - For now, just make sure these all call through this one function.
-    return coord.units.num2date(time)
+    return coord.units.num2date(time, only_use_cftime_datetimes=True)
 
 
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