Importing `esmvalcore.experimental` gives deprecation warning for `esmvalcore.experimental.config`

[bouweandela]

>>> import esmvalcore.experimental
/home/bandela/src/esmvalgroup/esmvalcore/esmvalcore/experimental/_warnings.py:13: UserWarning: 
  Thank you for trying out the new ESMValCore API.
  Note that this API is experimental and may be subject to change.
  More info: https://github.com/ESMValGroup/ESMValCore/issues/498
/home/bandela/src/esmvalgroup/esmvalcore/esmvalcore/experimental/config/__init__.py:15: ESMValCoreDeprecationWarning: The module `esmvalcore.experimental.config` has been deprecated in ESMValCore version 2.8.0 and is scheduled for removal in version 2.9.0. Please use the module `esmvalcore.config` instead.

the deprecation warning should only be shown when importing esmvalcore.experimental.config.