Template plugin_ffi uses FFIgen and generates both the FFIgen inputs and the generated file.

We rolled FFIgen to 9.0.0 in https://github.com/flutter/flutter/pull/130494, which means a slight change to the generated file.

* https://github.com/dart-lang/ffigen/issues/619

Note, because of https://github.com/flutter/flutter/issues/105695, we run the test on the FFIgen repo rather than on the flutter CI.