Fix Import/Export protected branch access levels associated with user

What does this MR do and why?

This MR fixes an issue with Project Import/Export of protected branches that have user (or group) associated with them. Prior to this fix a protected branch that had merge or push access levels associated with users would fail to be imported due to the following exception:

ProtectedBranch::MergeAccessLevel#project delegated to protected_branch.project, but protected_branch is nil: #<ProtectedBranch::MergeAccessLevel id: nil, protected_branch_id: nil, access_level: 40, created_at: \"2022-11-24 03:27:59.574000000 +0000\"

The exception is raised due to a call to protected_refs_for_users_required_and_available callback which calls project that is delegated to protected_branch, but protected_branch is nil during the run of these validations (since we do not have a valid protected branch just yet).

The 'fix', which is more of a workaround, is to not run these callbacks, which is a common practice for Import/Export in order to get the records migrated. As I mentioned above, this callback is skipped because we don't have access to protected_branch or project when validations are ran against merge_access_levels & push_access_levels. So let's create them blindly, instead of completely failing.

Mentions #387014 (closed)

Screenshots or screen recordings

before	after
prot-before.mov	prot-after.mov

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