Scale back down the default Shared Secrets Job timeout

Summary

In !445 (merged), we increased the Shared Secrets Job timeout to address #625 (closed). When #625 (closed) is closed, we can restore the original timeout (300 * time.Second).

Acceptance criteria

• Shared Secrets default timeout is restored to 300 * time.Second
• test.sh is updated to reduce the max wait time in wait_until_gitlab_running (see !445 (comment 903289161))