Modifying less files and saving them using the web editor can raise
and error. The error is due to the way odoo save the modified file.

It extends the view containing the URL of the file by filtering views
related to the xml bundle id and keeping those that have the said URL
in their content.

This lookup fails to give just one result in case there are multiple
file containing the said URL. This fix change the filter from a
bare `if url in view.arch` to a correct xpath lookup.

The "/web/static/src/variables.less" less file was one of the
problematic files.

opw-1889794

closes odoo/odoo#30186