[Settings] Change 'character set' to plural from in Quick Accent settings

[PesBandi]

Summary of the Pull Request

Changes "Choose a character set" to "Choose character sets" since we can now choose more than one.

PR Checklist

• Closes: [Settings-QuickAccent] "Choose a character set" even though you can choose more than one. #36564
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end user facing strings can be localized
• Dev docs: No need
• New binaries: None
• Documentation updated: No need

Validation Steps Performed

[jaimecbernardo]

LGTM! Thank you.