Update validate-pyproject requirement from <0.17 to <0.19

Updates the requirements on [validate-pyproject](https://github.com/abravalheri/validate-pyproject) to permit the latest version.
- [Release notes](https://github.com/abravalheri/validate-pyproject/releases)
- [Changelog](https://github.com/abravalheri/validate-pyproject/blob/main/CHANGELOG.rst)
- [Commits](abravalheri/validate-pyproject@v0.0.1...v0.18)

---
updated-dependencies:
- dependency-name: validate-pyproject
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

setup.py

@@ -29,7 +29,7 @@
     "pyproject-fmt<1.8",
     "ruff<0.5",
     "sphinx-autobuild==2021.3.14",  # Newer versions stopped "watching" appropriately?
-    "validate-pyproject<0.17",
+    "validate-pyproject<0.19",
 ]
 
 docs_requires = [