Bump sphinx-issues from 5.0.1 to 6.0.0 (#1042)

Bumps [sphinx-issues](https://github.com/sloria/sphinx-issues) from 5.0.1 to 6.0.0.
- [Commits](sloria/sphinx-issues@5.0.1...6.0.0)

---
updated-dependencies:
- dependency-name: sphinx-issues
  dependency-version: 6.0.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

pyproject.toml

@@ -63,7 +63,7 @@ build-backend = "flit_core.buildapi"
 docs = [
   "webargs",
   "Sphinx==9.1.0",
-  "sphinx-issues==5.0.1",
+  "sphinx-issues==6.0.0",
   "furo==2025.12.19",
 ]