Deploy key with write access can force push a protected branch
### Summary
A deploy key with write access can force push a protected branch.
### Steps to reproduce
1. Setup a deploy key with write access in a non-empty repository.
2. Make sure (e.g.) the `master` branch is protected (e.g. merge/push restricted to maintainer).
3. Amend a commit.
4. Force push the diverged `master` using the deploy key with write access.
### Example Project
(Not project specific.)
### What is the current *bug* behavior?
Branch is force-updated despite protection.
### What is the expected *correct* behavior?
Forced push to protected branch should be denied.
### Relevant logs and/or screenshots
(None.)
### Output of checks
Observed both on GitLab.com and a hosted GitLab instance.
#### Results of GitLab environment info
(n/a)
#### Results of GitLab application Check
(n/a)
### Possible fixes
No known fix.
issue