Fix _stylefilterparams_geowebcache_dataset

[giohappy]

This method has an old bug that makes this block fail.

The bug was introduced in https://github.com/GeoNode/geonode/commit/7d07b84d3dac0613863050aa3d7b5758efc2cf14 when the response content variable _ was removed. This has broken the XML parsing a few lines below. A content receiver was reintroduced lately, to make flake8 happy, but the bug was still there.

While this bug is fixed the effectiveness of these calls should be analyzed:

1 - we don't need to set the styleParameterFilter for GWC on every update 2 - do we really need to invalidate GWC on every update?

https://github.com/GeoNode/geonode/blob/9ca2f13a083e9ca37cd368106864f32e33176499/geonode/geoserver/helpers.py#L1643C1-L1667