Remove deprecated `merge: strict` from Mergify.yml
Remove deprecated `merge: strict` from Mergify.yml

Remove `merge: strict` from the Mergify configuration because it is
deprecated:

> The configuration uses the deprecated strict mode of the merge action.
> A brownout is planned for the whole December 6th, 2021 day.
> This option will be removed on January 10th, 2022.
> For more information: https://blog.mergify.com/strict-mode-deprecation/

asbjornu/GitVersion,gep13/GitVersion,gep13/GitVersion,GitTools/GitVersion,asbjornu/GitVersion,GitTools/GitVersion