Python dependency: Bump fixtures from 4.2.5 to 4.2.6 in /web/regression

Bumps [fixtures](https://github.com/testing-cabal/fixtures) from 4.2.5 to 4.2.6.
- [Changelog](https://github.com/testing-cabal/fixtures/blob/master/NEWS)
- [Commits](testing-cabal/fixtures@4.2.5...4.2.6)

---
updated-dependencies:
- dependency-name: fixtures
  dependency-version: 4.2.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

web/regression/requirements.txt

@@ -22,7 +22,7 @@
 # relevant packages.
 ###########################################################
 extras==1.0.0
-fixtures==4.2.5
+fixtures==4.2.6
 linecache2==1.0.0
 pbr==6.1.1
 pycodestyle>=2.5.0