gh-70647: Add detail to error message when parsing a bad day of month.

[gpshead]

The presence of the values in the error message gives a stronger hint as to what went wrong.

>>> datetime.strptime("2.29", "%m.%d")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    datetime.strptime("2.29", "%m.%d")
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File ".../Lib/_strptime.py", line 565, in _strptime_datetime
    return cls(*args)
           ~~~^^^^^^^
ValueError: day 29 is out of range for month 2 in year 1900

• Issue: datetime.strptime without a year fails on Feb 29 #70647

[pitrou]

+1 on the principle, but ideally there would be a test for this.