The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The given package appears to have a Python development package (python3-dev, python3-all-dev or pythonX.Y-dev) listed in its Build-Depends or Build-Depends-Indep fields, but only "Architecture: all" packages are built by this source package. Python applications and modules do not usually require those dev packages, so you should consider removing them in favour of python3, python3-all or pythonX.Y.
If you are building a Python extension instead, you should have development packages listed in Build-Depends, but normally there should be at least one Architecture: any package.