Update wagtail requirement from >=4.1 to >=7.4

Updates the requirements on [wagtail](https://github.com/wagtail/wagtail) to permit the latest version.
- [Release notes](https://github.com/wagtail/wagtail/releases)
- [Changelog](https://github.com/wagtail/wagtail/blob/main/CHANGELOG.txt)
- [Commits](wagtail/wagtail@v7.0...v7.4)

---
updated-dependencies:
- dependency-name: wagtail
  dependency-version: '7.4'
  dependency-type: direct:production
...

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

Author: dependabot[bot]

sandbox/requirements.txt

@@ -1,4 +1,4 @@
 Django>=3.2
-wagtail>=4.1
+wagtail>=7.4
 django-debug-toolbar==3.2.2
 -e .[docs,test]