ignore warnings at import time in astrometry.net

[keflavich]

addresses issue astropy#1544 by explicitly ignoring warnings when the instance of the astrometry.net class is created at import time.

[keflavich]

this wasn't supposed to be a PR onto my own branch, but after thinking more, I don't think we should make this change

[codecov-commenter]

Codecov Report

Merging #18 (4738822) into main (5ca7593) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #18   +/-   ##
=======================================
  Coverage   67.05%   67.05%           
=======================================
  Files         411      411           
  Lines       27212    27212           
=======================================
  Hits        18248    18248           
  Misses       8964     8964           

Impacted Files	Coverage Δ
astroquery/astrometry_net/core.py	50.52% <100.00%> (ø)

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[bsipocz]

but after thinking more, I don't think we should make this change

no, I don't think we should suppress this warning. Users should do it on their end, or rather get an API key.