build: Fix CustomTarget initializer annotation
build: Fix CustomTarget initializer annotation

the `output` parameter is a string, not an int.

pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson