AwesomeWM does not recognize virtual monitors added by xrandr 1.5.

Output of awesome --version:

awesome v4.3 (Too long)
 • Compiled against Lua 5.3.5 (running with Lua 5.3)
 • D-Bus support: ✔
 • execinfo support: ✔
 • xcb-randr version: 1.6
 • LGI version: 0.9.2

How to reproduce the issue:

Xrandr 1.5 adds support for virtual monitors, which should be respected by awesomewm (see #823).

However, if I split my screen in two halves using:

xrandr --setmonitor DP2~1 1280/300x1440/168+0+0 DisplayPort-2
xrandr --setmonitor DP2~2 1280/300x1440/168+1280+0 none

and then restart awesomewm (default config, no X restart), only the first (left) monitor/screen is detected. I can however move windows to the 2nd (right) half, yet new windows won't open nor do I get a 2nd wibar etc.

Actual result:

Only one screen is detected and used by awesomewm.

Expected result:

Two screens should be detected and used and get their own wibar/tags.