Fix backup restore

What does this MR do?

This MR fixes the backup restore task.

Are there points in the code the reviewer needs to double check?

Whether the mode 0277 makes sense. (Group SUID + group/user read/write permissions)

Why was this MR needed?

86359ec8 broke this, and it was not caught by any specs. Users would see:

Restoring repositories ...
rake aborted!
NameError: undefined local variable or method `repos_path' for #<Backup::Repository:0x00000007cea1d8>
/opt/gitlab/embedded/service/gitlab-rails/lib/backup/repository.rb:59:in `restore'
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/backup.rake:79:in `block (4 levels) in <top (required)>'
/opt/gitlab/embedded/service/gitlab-rails/lib/tasks/gitlab/backup.rake:54:in `block (3 levels) in <top (required)>'
Tasks: TOP => gitlab:backup:repo:restore
(See full trace by running task with --trace)

What are the relevant issue numbers?

#20188 (closed)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

mentioned in issue #20188 (closed)

mentioned in issue #19582 (closed)

Added 1 commit:

• c07f8f2e - Checkout gitlab-shell

Changed title: Fix backup restore and add CI tests → Fix backup restore

Added 1 commit:

• 8469f9e0 - Fix backup restore

Marked the task Branch has no merge conflicts with master (if you do - rebase it please) as completed

Marked the task Conform by the style guides as completed

Marked the task All builds are passing as completed

Marked the task Squashed related commits together as completed

Marked the task CHANGELOG entry added as completed

Milestone changed to %8.10

Added ~149423 label

Added 1 commit:

• da12adc3 - Set permissions of backup dir to g+s

Added 17 commits:

• da12adc3...83180110 - 15 commits from branch master
• 4fb3b9bf - Fix backup restore
• a1f07a86 - Set permissions of backup dir to g+s

Reassigned to @rymai

Added 16 commits:

• a1f07a86...89872574 - 15 commits from branch master
• c6ff77d4 - Fix backup restore

Status changed to merged

mentioned in commit c4ba2b15

mentioned in issue #20242 (closed)

when will this released via the omnibus packages?