No source packages in APT repo?

I added a deb-src entry to my APT config matching the deb entry:

deb https://repo.dovecot.org/ce-2.3-latest/ubuntu/focal focal main deb-src https://repo.dovecot.org/ce-2.3-latest/ubuntu/focal focal main

When this is there, I see a warning when running "apt update".

W: Skipping acquire of configured file 'main/source/Sources' as repository 'https://repo.dovecot.org/ce-2.3-latest/ubuntu/focal focal InRelease' does not seem to provide it (sources.list entry misspelt?)

Were source packages excluded deliberately?  The github repo for dovecot does not have a "debian" directory, which is the other route that would allow me to build packages.

Thanks, Shawn