build(deps): bump fixtures from 3.0.0 to 4.0.0

Bumps [fixtures](https://github.com/testing-cabal/fixtures) from 3.0.0 to 4.0.0.
- [Release notes](https://github.com/testing-cabal/fixtures/releases)
- [Changelog](https://github.com/testing-cabal/fixtures/blob/master/NEWS)
- [Commits](https://github.com/testing-cabal/fixtures/compare/3.0.0...4.0.0)

---
updated-dependencies:
- dependency-name: fixtures
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

requirements.txt

@@ -17,7 +17,7 @@ ecdsa==0.17.0
 extras==1.0.0
 feedgen==0.9.0
 feedparser==6.0.8
-fixtures==3.0.0
+fixtures==4.0.0
 Flask==2.1.1
 Flask-Caching==1.10.1
 flask-gae-static==0.2