meson: always install bash-completion file

Currently we install the file only when bash-completion is found.
There's little point in that - one can install it at a later stage.

This gets up on par with the cmake build.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit b0bedb5a)
3 jobs for maint-1.6 in 49 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container
passed #6734957
container

00:00:11

 
  Build
passed #6734959
cmake

00:00:22

passed #6734958
meson

00:00:37