Loosen argument type in callback (dart-lang/stack_trace#65)

The type was technically changed when refactoring to function type
syntax, restore the `dynamic` but make it explicit.

This surfaces as a static problem in the null safety branch. Fix it on
the master branch as well for consistency.
1 file changed
tree: c101cdeceaaf1bddf595d38c3d50ce20b1234b57
  1. pkgs/