Resolve "Resolve auto-correctable RuboCop offenses (Exclude-only) in .rubocop_todo/**/*.yml"

What does this MR do and why?

This MR removes a redundant return in the Authentication#login method in lib/gitlab/auth/database/authentication.rb to comply with the Style/RedundantReturn RuboCop rule. The change does not affect functionality but ensures consistent code style across the codebase.

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Related issue :#239356

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Related to #239356