Change Hint Mode of LeibnizEquiv

As discussed in iris!966 (merged), the LeibnizEquiv typeclass currently has Hint Mode ! -, signifying that the type is an input, while the equivalence which is supposed to imply leibniz equality is an output. That should be Hint Mode ! !, i.e., both are inputs.

enabled an automatic merge when the pipeline for faa43c7a succeeds

Thank you! Merging.

merged

mentioned in commit 800125de