In de26d148, we added support
for the `--introspection-dump` CLI flag inside GApplication
but that initialized a bunch of classes that e.g. try to migrate config files.
Let’s move it to the beginning of the main program entry point before
GApplication is even created to avoid having to set `HOME` in the Nix package
(introduced in 15f61da9)
and prevent warnings about data files not being installed.