Add user mendel to group render.

The render group is created by systemd and membership is required to
use DRM render nodes.

This was changed in buster:
https://salsa.debian.org/systemd-team/systemd/commit/e3772a013721083a740ab9dedbf060cf5b3c3709

BUG: 144855296
Change-Id: I5976afbadc5d80f4ff7d602dc8874b82a5f69f65
diff --git a/etc/runonce.d/00-rootfs-cleanups b/etc/runonce.d/00-rootfs-cleanups
index 263e14a..c736b51 100755
--- a/etc/runonce.d/00-rootfs-cleanups
+++ b/etc/runonce.d/00-rootfs-cleanups
@@ -26,7 +26,7 @@
 udevadm control --reload-rules
 udevadm trigger
 
-MENDEL_GROUPS="adm audio bluetooth games i2c input plugdev staff sudo users video netdev systemd-journal apex"
+MENDEL_GROUPS="adm audio bluetooth games i2c input plugdev staff sudo users video netdev systemd-journal apex render"
 
 for i in $MENDEL_GROUPS; do
     echo "runonce: adding mendel to $i" 2>&1 >>/var/log/rootfs-cleanups.log