Bump pipenv from 2026.6.2 to 2026.7.1

Bumps [pipenv](https://github.com/pypa/pipenv) from 2026.6.2 to 2026.7.1.
- [Release notes](https://github.com/pypa/pipenv/releases)
- [Changelog](https://github.com/pypa/pipenv/blob/main/CHANGELOG.md)
- [Commits](pypa/pipenv@v2026.6.2...v2026.7.1)

---
updated-dependencies:
- dependency-name: pipenv
  dependency-version: 2026.7.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -29,7 +29,7 @@ MarkupSafe==3.0.3
 mccabe==0.7.0
 mysqlclient==2.2.8
 packaging==26.2
-pipenv==2026.6.2
+pipenv==2026.7.1
 platformdirs==4.11.0
 pluggy==1.6.0
 Pygments==2.20.0