Call to undefined method getTableMapping() on metatag_update_8109

Problem/Motivation

Hello,
There is a problem at the update database if there are modules on project that do not implement SqlEntityStorageInterface (like for example external_entity).
In the hook update 8109 and in metatag.post_update.php, we get the storage and try to call the method getTableMapping() on it.
We should check before if the storage implements the interface SqlEntityStorageInterface, and call getTableMapping() only if it is the case.

Proposed resolution

I purpose a patch that fixes it.