buildDartApplication: Declare dependency sources as build inputs

pkgs/build-support/dart/build-dart-application/default.nix

···
       darwin.sigtool
     ];
 
+    buildInputs =
+      # Ensure that we inherit the propagated build inputs from the dependencies.
+      builtins.attrValues pubspecLockData.dependencySources;
+
     preConfigure = args.preConfigure or "" + ''
       ln -sf "$pubspecLockFilePath" pubspec.lock
     '';