Fix: Only rescan when bitbake settings are changed

[deribaucourt]

The extension started scanning twice at startup. It turns out this was because the extension was sending a rescan request when the python embedded settings where updated. This was fixed by only sending a rescan request when the bitbake settings are changed.

[WilsonZiweiWang]

so somehow the python extension setting change triggered the config change event in our language server? That's an odd behaviour. but anyway, the extra scan is gone. Good job!