systemd: update 251.4 -> 251.8

This resolves systemd-boot fails with latest meson,
while systemd -> 252 is being prepared.

(From OE-Core rev: 1d96287906f66ad28e50c9686eaffc2fb7b874fe)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/systemd/systemd.inc

@@ -14,7 +14,7 @@ LICENSE = "GPL-2.0-only & LGPL-2.1-only"
 LIC_FILES_CHKSUM = "file://LICENSE.GPL2;md5=751419260aa954499f7abaabaa882bbe \
                     file://LICENSE.LGPL2.1;md5=4fbd65380cdd255951079008b364516c"
 
-SRCREV = "2a674b4b66af1a050a0362b646d2fca90c90112e"
+SRCREV = "ae8b249af4acb055f920134f2ac584c4cbc86e3b"
 SRCBRANCH = "v251-stable"
 SRC_URI = "git://github.com/systemd/systemd-stable.git;protocol=https;branch=${SRCBRANCH} \
 "