Defer call to set_break_language

[Naros]

Fixes #86816

As ScriptExtension objects are not yet set up when this is called to invoke virtuals, by using call_deferred, we avoid this error:

ERROR: Required virtual method ScriptExtension::_get_language must be overridden before calling.
   at: _gdvirtual__get_language_call (./core/object/script_language_extension.h:106)

[vnen]

I wonder if there's a better time to do this, maybe some other notification. But I cannot think of anything at the moment, so this is a good compromise.

[akien-mga]

Thanks!