status/keyboard: Always released held keyboard after activating source

status/keyboard: Always released held keyboard after activating source

As the keyboard is released asynchronously after setting the ibus
engine, there's a possibility that the `this._reloading` property
changed in the meantime.

To ensure that `holdKeyboard()` and `releaseKeyboard()` are correctly
paired, record the condition in a local variable so that it maintains
its value in the callback.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3476>