Update approvaltests requirement from >=18.0.5 to >=18.1.0

Updates the requirements on [approvaltests](https://github.com/approvals/ApprovalTests.Python) to permit the latest version.
- [Release notes](https://github.com/approvals/ApprovalTests.Python/releases)
- [Commits](approvals/ApprovalTests.Python@v18.0.5...v18.1.0)

---
updated-dependencies:
- dependency-name: approvaltests
  dependency-version: 18.1.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -12,5 +12,5 @@ rellu >= 2.0.2
 twine
 wheel
 typing-extensions >= 4.15.0
-approvaltests >= 18.0.5
+approvaltests >= 18.1.0
 mypy == 2.1.0