Resolve astropy 4.2.1 FITS header warning

[eslavich]

A handful of tests in the warnings-as-exceptions job began failing with the release of astropy 4.2.1:

E                       astropy.io.fits.verify.VerifyWarning: Error validating header for HDU #0 (note: Astropy uses zero-based indexing).
E                           Header size is not multiple of 2880: 1246
E                       There may be extra bytes after the last HDU or the file is corrupted.

It looks like some of the test data we have checked into the repo needs to be regenerated