Bump hyperkitty from 1.3.7 to 1.3.8 in /web

Bumps [hyperkitty](https://gitlab.com/mailman/hyperkitty) from 1.3.7 to 1.3.8.
- [Release notes](https://gitlab.com/mailman/hyperkitty/tags)
- [Commits](https://gitlab.com/mailman/hyperkitty/compare/1.3.7...v1.3.8)

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

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

web/requirements.txt

@@ -1,4 +1,4 @@
 mailmanclient==3.3.5
 postorius==1.3.8
-hyperkitty==1.3.7
+hyperkitty==1.3.8
 django-mailman3==1.3.11