Bump testfixtures from 6.10.3 to 6.15.0 (#2049)
Bump testfixtures from 6.10.3 to 6.15.0 (#2049)

Bumps [testfixtures](https://github.com/Simplistix/testfixtures) from 6.10.3 to 6.15.0.
- [Release notes](https://github.com/Simplistix/testfixtures/releases)
- [Changelog](https://github.com/Simplistix/testfixtures/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/Simplistix/testfixtures/compare/6.10.3...6.15.0)

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

Co-authored-by: dependabot-preview[bot] <6a4c1c4838f800d1998274cd5234e1f65c55e90c@users.noreply.github.com>
modoboa/modoboa,bearstech/modoboa,modoboa/modoboa,bearstech/modoboa,modoboa/modoboa,bearstech/modoboa,modoboa/modoboa,bearstech/modoboa