The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
The package is architecture-dependent, ships a pkg-config file in a
public, architecture-dependent pkg-config search path and is marked
Multi-Arch: foreign. pkg-config will be unable to find this file,
unless it is installed for a matching architecture, but the
marking says that the architecture should not matter.
Please remove the
Multi-Arch: foreign stanza.