fix: update updater cbindgen toml inputs after upstream API split

Upstream commit be89e40 (#138) split the updater C API into
separate engine and dart cbindgen configs (cbindgen_engine.toml /
cbindgen_dart.toml) and removed the combined cbindgen.toml, but the
companion shell/common/shorebird/BUILD.gn change to update the
declared inputs was not landed. Without this fix, the iOS engine
build fails with:
  ninja: error: '../../flutter/third_party/updater/library/cbindgen.toml',
  needed by 'gen/flutter/shell/common/shorebird/rust_updater_<...>.stamp',
  missing and no known rule to make it

Worth landing upstream as a follow-up on #138.

Author: bdero

engine/src/flutter/shell/common/shorebird/BUILD.gn

@@ -86,7 +86,8 @@ if (shorebird_updater_supported) {
       "$shorebird_updater_dir/Cargo.lock",
       "$shorebird_updater_dir/library/Cargo.toml",
       "$shorebird_updater_dir/library/build.rs",
-      "$shorebird_updater_dir/library/cbindgen.toml",
+      "$shorebird_updater_dir/library/cbindgen_dart.toml",
+      "$shorebird_updater_dir/library/cbindgen_engine.toml",
       "$shorebird_updater_dir/library/.cargo/config.toml",
     ]
     inputs += shorebird_updater_rs_sources