Bump wagtail from 5.2.3 to 5.2.6 in /requirements

Bumps [wagtail](https://github.com/wagtail/wagtail) from 5.2.3 to 5.2.6.
- [Release notes](https://github.com/wagtail/wagtail/releases)
- [Changelog](https://github.com/wagtail/wagtail/blob/main/CHANGELOG.txt)
- [Commits](wagtail/wagtail@v5.2.3...v5.2.6)

---
updated-dependencies:
- dependency-name: wagtail
  dependency-type: direct:production
...

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

requirements/base.txt

@@ -28,6 +28,6 @@ six==1.16.0
 ua-parser==0.18.0
 unicodecsv==0.14.1
 vcrpy==6.0.1 # recoding Salesforce interactions in tests
-wagtail==5.2.3
+wagtail==5.2.6
 wagtail-modeladmin==2.0.0
 whitenoise==6.6.0