wrap: Track libadwaita 1.2

Initial Setup doesn't currently need a newer version, but previously
when the wrap fallback was used, libadwaita main would be built. Main
depends on a newer gtk4 than is in the CI image, and so CI fails:

    libadwaita| Dependency gtk4 found: NO found 4.6.6 but need: '>= 4.9.1'
    libadwaita| Run-time dependency gtk4 found: NO
    subprojects/libadwaita/src/meson.build:247:0: ERROR: Invalid version of dependency, need 'gtk4' ['>= 4.9.1'] found '4.6.6'.

Track the stable branch of libadwaita instead.

(cherry picked from commit f0e041fb)