ci: bump lxml dev dependency to 5.3 for Python 3.13

lxml 4.9.x has no wheels for Python 3.13 and fails to build
from source without libxml2-dev. Bumped to 5.3.0 which ships
3.13 wheels. This is a dev-only dependency with zero imports
in the codebase.

OBS-1999

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: aarthy-dk

pyproject.toml

@@ -50,7 +50,7 @@ dependencies = [
 dev = [
     "ruff~=0.7.3",
     "invoke~=2.1.2",
-    "lxml~=4.9.1",
+    "lxml~=5.3.0",
     "mypy~=1.5.0",
     "pre-commit~=2.20.0",
     "pytest-cov~=4.0.0",