vizier: add precisions about query_object

[ManonMarchand]

Hello astroquery maintainers,

This tries to solve the documentation issue #3509

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.39%. Comparing base (e1aa370) to head (81f2ac5).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3527   +/-   ##
=======================================
  Coverage   72.39%   72.39%           
=======================================
  Files         219      219           
  Lines       20432    20432           
=======================================
  Hits        14792    14792           
  Misses       5640     5640           

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[bsipocz]

Thanks!