Bump mistletoe from 1.0.1 to 1.2.1 in /caster-back

Bumps [mistletoe](https://github.com/miyuchina/mistletoe) from 1.0.1 to 1.2.1.
- [Release notes](https://github.com/miyuchina/mistletoe/releases)
- [Changelog](https://github.com/miyuchina/mistletoe/blob/master/cutting-a-release.md)
- [Commits](miyuchina/mistletoe@v1.0.1...v1.2.1)

---
updated-dependencies:
- dependency-name: mistletoe
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

caster-back/requirements.txt

@@ -7,7 +7,7 @@ strawberry-graphql-django==0.9.4
 strawberry-graphql[channels]<=0.177.0
 strawberry-django-plus==2.5.0
 django-cors-headers==4.0.0
-mistletoe==1.0.1
+mistletoe==1.2.1
 pydantic==1.10.7
 channels-redis==4.1.0
 sentry-sdk==1.29.0