Incorrect severity level

[zypA13510]

When running xmllint myXML.xml, the result is:

myXML.xml:4: namespace warning : xmlns: URI my.short.namespace is not absolute

This warning can be suppressed when running xmllint --nowarning myXML.xml.

However, this warning is displayed as severity: Error inside the linter panel, and marked in the XML file as such. AFAIK we do have severity info/warning/error from the linter package API, so we should mark it according to the output from xmllint.

I'm not sure if all xmllint output follows the same format (just started using it). If it is, this can be easily fixed, I think?