grep -L exit status reverted

After upgrading to Ubuntu 20.04LTS (grep 3.1-2build1 => 3.4-1), the following code snippet stopped working:

# All patches must have "From:", "Date:", and "Subject:" lines
for hdr in From Date Subject; do
    grep -L ^$hdr: $dir/* || ( echo Missing \"$hdr:\" line; exit -1 )
done

It looks like this was fixed upstream, cfr. "Revert -L exit status change introduced in grep 3.2"
(https://git.savannah.gnu.org/cgit/grep.git/commit/?id=0435ebca64fbafcd62008c991dd9377d8a792dfc)