Allow LST evaluation to fail when making FITS time cards.

This is yet another astropy IERS thing. astropy 4.0.2.

When the mcsActor gets the time cards from the ics.utils routines, we get a familiar astropy error: "(some) times are outside of range covered by IERS table.", but in an unfamiliar context.

Calling the same routines directly, as the same user on the same host (pfs-data@mcs), the timecards routines work fine:

In [1]: from ics.utils.fits import timecards
In [2]: import time
In [3]: tc = timecards.TimeCards()
In [4]: tc.end()
In [5]: tc.getCards()
[good stuff]

Not quite sure where the problem is. But we cannot lose the primary time cards when getting something as unimportant as LST. I propose to wrap the LST in an except and live without LST.

Maybe the astropy 5 in rubin3 will fix that, but we cannot test under the current circumstances.