.builds: re-add sway on Debian

It passes now, thanks to the recent work to add retries to screenshots.

If it turns out to still not be reliable enough, we can look at this
again.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

.builds/linux.yml

@@ -18,7 +18,7 @@ packages:
  - xvfb
  - xdotool
  - scrot
- # - sway TODO: uncomment once the wayland e2e test passes again
+ - sway
  - grim
 sources:
  - https://git.sr.ht/~eliasnaur/gio