DM-14770: tests mis-call PropertySet.get

[r-owen]

No description provided.

[PaulPrice]

It's annoying we can't simply say "failDecEndCpuTime" in addMultTask, but this works.

[ktlim]

We could define a __contains__ method, but I'm a little wary of having PropertySet fall into the uncanny valley of being sort of like a dict but not exactly. (And exactitude is tricky given the need for C++ usage.)

[RobertLuptonTheGood]

I know that KT has pushed to *not* make PropertySet look like a dict, but I am ever-less convinced that he's right on this (I'd be interested in @jbosch's opinion). The gratuitous differences are irritating and a source of difficulty. I am aware that there's an `toDict` method, but the mere fact that this exists to provide a different interface with no extra functionality suggests that we should just make a PropertySet look 95% like a dict.

[TallJimbo]

My (not deeply considered) $0.02 on this is that the associative container we use to directly represent (and especially round-trip) FITS headers shouldn't try to be too dict-like, but we should probably have another class that is both usable in C++ and a true Mapping (i.e. be completely dict-like) in Python.

But I'd like to review the places we want to use these before really committing to that opinion.

[r-owen]

I'm uneasy about making PropertySet and PropertyList too dict-like due to serious internal differences that make it a poor mental model. That said __contains__ seems reasonable. I think DM-13222 will help a bit by getting rid of the asArray argument to get (which can too easily be mistaken for a default argument, as per this ticket).

I wish we could use a different container for FITS header cards. PropertyList has some unfortunate limitations there (e.g. no support for missing values, no ability to COMMENT cards and such in the original order).