oniro-linux.conf: Specify preferred version of pyyaml

Homeassistant requires pyyaml == 5.3 while oe layer provides newer
version. Specifying preferred older version to fix the broken
dependencies.

Fixes: https://booting.oniroproject.org/distro/oniro/-/issues/187


Signed-off-by: Pavel Zhukov <pavel.zhukov@huawei.com>