:no-heading: raises "WARNING: Title level inconsistent"

E.g. trying it in astroquery.mast (it was part of an experiment only)

```
Reference/API
=============

.. automodapi:: astroquery.mast
:no-heading:
:no-inheritance-diagram:
```

I get this warning:
```
/Users/bsipocz/munka/devel/astroquery/docs/mast/mast.rst:758: WARNING: Title level inconsistent:

Classes
^^^^^^^
```

Generated summary with no heading:

vs with the heading on:

Reproduce the warning from the `astroquery.mast` example in `docs/mast/mast.rst` around line 758, focusing on the `automodapi` directive with `:no-heading:`. Trace how the directive generates the Classes section and confirm completion when the example builds without the title-level warning while retaining the intended no-heading output.

Written by the indexing model from the issue text.