Pin pandas to avoid broken round function

[schlunma]

Description

This PR fixes recent test failures that are caused by a bug in pandas. This bug breaks the round function that we use to round to the nearest second:

ESMValCore/esmvalcore/cmor/_fixes/icon/icon.py

Lines 495 to 497 in d6008f3

	new_datetimes = (year_month_day + day_float).round(
	'S'
	).dt.to_pydatetime()

In addition, this removes the use of two deprecated features:

1. Replace 'S' by 's' (see https://pandas.pydata.org/pandas-docs/stable/user_guide/timeseries.html#offset-aliases)
2. Surround DatetimeProperties.to_pydatetime by np.array as recommended in the deprecation message. Unfortunately, this does not remove the warning, but hopefully this will avoid problems in the future.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d6008f3) 93.72% compared to head (9b020f0) 93.72%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2305   +/-   ##
=======================================
  Coverage   93.72%   93.72%           
=======================================
  Files         238      238           
  Lines       13122    13123    +1     
=======================================
+ Hits        12299    12300    +1     
  Misses        823      823           

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[valeriupredoi]

cheers, Manu! Always helpful to add refs to issue or PR numbers when we pin deps 👍

[valeriupredoi]

many thanks, Manu 🍺