Bump mastodon-py from 1.6.3 to 1.8.1

Bumps [mastodon-py](https://github.com/halcy/Mastodon.py) from 1.6.3 to 1.8.1.
- [Release notes](https://github.com/halcy/Mastodon.py/releases)
- [Changelog](https://github.com/halcy/Mastodon.py/blob/master/CHANGELOG.rst)
- [Commits](halcy/Mastodon.py@1.6.3...1.8.1)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,4 +1,4 @@
-Mastodon.py==1.6.3
+Mastodon.py==1.8.1
 tomli==2.0.1
 tracery==0.1.1
 tweepy==4.12.1