Fix code scanning alert - Potentially unsafe external link

[rlskoeser]

Tracking issue for:

• https://github.com/Princeton-CDH/mep-django/security/code-scanning/5
• https://github.com/Princeton-CDH/mep-django/security/code-scanning/4
• https://github.com/Princeton-CDH/mep-django/security/code-scanning/3
• https://github.com/Princeton-CDH/mep-django/security/code-scanning/2
• https://github.com/Princeton-CDH/mep-django/security/code-scanning/7
• https://github.com/Princeton-CDH/mep-django/security/code-scanning/6