Error in rendering of token names in notification email

What does this MR do and why?

Fixes #432518 (closed)

Error in rendering of token names

A bot user can have one pat at any point of time. ExpiringWorker is written on the same premise and we expect the user of type bot to have only one pat. This mailer need not be an exception and run a loop on multiple token names

We are also change method name to sound more meaningful in case of resource access tokens and also the email text for access token expiring notification

MR acceptance checklist

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Screenshots or screen recordings

Mails being sent after the bug fix

How to set up and validate locally

1. Create a Resource access token for a group or a project and set expiry date < than 7 days
2. Open gdk rails console and execute PersonalAccessTokens::ExpiringWorker.new.perform
3. The worker should execute and owner of the group should receive email. In case of local setup mail should appear in /rails/letter_opener