Bump ruff from 0.15.17 to 0.15.20 in /mailbox-app

Bumps [ruff](https://github.com/astral-sh/ruff) from 0.15.17 to 0.15.20.
- [Release notes](https://github.com/astral-sh/ruff/releases)
- [Changelog](https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md)
- [Commits](astral-sh/ruff@0.15.17...0.15.20)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

mailbox-app/requirements/constraints.txt

@@ -16,7 +16,7 @@ pytest==9.1.1
 pytest-cov==7.0.0
 pytest-django==4.12.0
 python-dotenv==1.2.2
-ruff==0.15.17
+ruff==0.15.20
 sqlparse==0.5.5
 webencodings==0.5.1
 whitenoise==6.11.0

mailbox-app/requirements/development.txt

@@ -5,4 +5,4 @@ pip-audit==2.10.0
 pytest==9.1.1
 pytest-cov==7.0.0
 pytest-django==4.12.0
-ruff==0.15.17
+ruff==0.15.20