build(deps): bump testtools from 2.5.0 to 2.6.0

Bumps [testtools](https://github.com/testing-cabal/testtools) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/testing-cabal/testtools/releases)
- [Changelog](https://github.com/testing-cabal/testtools/blob/master/NEWS)
- [Commits](https://github.com/testing-cabal/testtools/compare/2.5.0...2.6.0)

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

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

requirements.txt

@@ -74,7 +74,7 @@ rsa==4.9
 sgmllib3k==1.0.0
 six==1.16.0
 soupsieve==2.4
-testtools==2.5.0
+testtools==2.6.0
 tlslite-ng==0.7.6
 tweepy==4.13.0
 ujson==5.7.0