fix: TypeError exception during student.send_activation_email task

[DmytroAlipov]

Description

backport from master

TypeError exception during student.send_activation_email task

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[mphilbrick211]

Hi @openedx/vanguards! Is this something you could review and merge for us? Apologies if you are not the appropriate team.

[mphilbrick211]

Thanks so much, @zainab-amir! Are you also able to merge?

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