It seems that your patch has been added[1] to the walnascar-nut branch
(which is a staging branch for Walnascar). It has however most probably
missed the merge window for version 5.2.1 by a couple of days. The next
Walnascar release, 5.2.2 is expected to be released mid-July.

[1]:
https://git.openembedded.org/openembedded-core-contrib/commit/meta/classes-recipe/systemd.bbclass?h=stable/walnascar-nut&id=ea207dce1f5f8579d8ddde487ac9852f50bfc792

Thanks for the update Gyorgy. I was expecting it to appear within https://git.yoctoproject.org/poky/log/?h=walnascar-next but was obviously wrong. Out of curiosity, is this process described anywhere?