Addressing some PHP8 incompatibilities - Diffusion & Differential

Summary: Running through setting up and using Diffusion repositories and addressing PHP8 issues that come up.

Test Plan:
I set up a hosted mercurial repository and pushed commits to it over ssh.
I set up a hosted git repository and pushed commits to it over ssh.
I set up a mirrored mercurial repository over ssh.
I set up a mirrored git repository over ssh.

I created a diff on a git repository and landed it.
I created a diff on a mercurial repository and landed it.

I cloned and pushed a commit to a mercurial repo over http.
I cloned and pushed a commit to a git repo over http.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D21864