Add python-is-python3 apt to apt-requirements.txt

It turns out we actually depend on that but it's not installed by
default on Ubuntu 22.04 LTS.

Signed-off-by: Pirmin Vogel <[email protected]>

Author: vogelpi

apt-requirements.txt

@@ -46,6 +46,7 @@ python3-pip
 python3-setuptools
 python3-urllib3
 python3-wheel
+python-is-python3
 srecord
 tree
 xmlstarlet