Make sure the gir target is added to the dependency

Also clean up some variable names to match our other projects.

Testing Done:
Ran the following without issue

```
meson setup --wipe -Dintrospection=false -Ddoc=false build-no-introspection
ninja -C build-no-introspection/ turtles
```

Reviewed at https://reviews.imfreedom.org/r/2952/