[pip](deps-dev): Update towncrier requirement in the dev-deps group (#580)

Updates the requirements on [towncrier](https://github.com/twisted/towncrier) to permit the latest version.

Updates `towncrier` to 25.8.0
- [Release notes](https://github.com/twisted/towncrier/releases)
- [Changelog](https://github.com/twisted/towncrier/blob/trunk/NEWS.rst)
- [Commits](twisted/towncrier@24.8.0...25.8.0)

---
updated-dependencies:
- dependency-name: towncrier
  dependency-version: 25.8.0
  dependency-type: direct:development
  dependency-group: dev-deps
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements-dev.txt

@@ -6,7 +6,7 @@ lefthook>=1.8.4,<2
 pyright[nodejs]>=1.1.389,<2
 ruff>=0.8.0,<1
 tox>=4.23.2,<5
-towncrier>=24.8.0,<25
+towncrier>=24.8.0,<26
 
 # Documentation utilities