Unbreak build with Meson 0.61.0

See https://github.com/mesonbuild/meson/issues/9441. Tested downstream.

$ meson setup _build
[...]
data/appdata/meson.build:2:0: ERROR: Function does not take positional arguments.

http://www.ipv6proxy.net/go.php?u=http://package18.nyi.freebsd.org/data/122amd64-default-foo/2022-01-20_18h39m40s/logs/errors/polari-41.0.log