Plaintext emails rendered from templates contain escaping

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

1. Send any email using a text (not HTML) template, where one of the context variables being rendered contains special characters (&,<,>,',etc)

### Expected Result

1. Email renders as straightforward plaintext without any form of escaping

### Actual Result

Email is rendered with inappropriate escaping that's not needed

### Product Area

Other

### Link

_No response_

### DSN

_No response_

### Version

_No response_