sysutils/accountsservice: unbreak update to 0.6.55

In ffb1311e56725702208e807cfc63c8163c6b4a52 the port was updated to
0.6.55, which unfortunately broke some functionality in gdm.

Add the patch from OpenBSD to fix this.

Reported by: rm
Obtained from: https://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/ports/sysutils/accountsservice/patches/patch-src_libaccountsservice_act-user-manager_c
PR: 249445

(cherry picked from commit fa6b589dc7cf40675fad8764fd86788107e085e7)