Fix the build system when introspection is disabled
Review Request #2951 — Created Feb. 10, 2024 and discarded — Latest diff uploaded
With introspection turned off birb_gir was undefined, this fixes that.
ran the following without issue
meson setup --wipe -Dintrospection=false -Ddoc=false build-no-introspection ninja -C build-no-introspection turtles