Exclude Python 3.13 + Plone 6.0 from CI matrix

Python 3.13 support was added in Plone 6.1, so this combination
is not supported. The tests fail with ComponentLookupError for
views and ConstraintNotSatisfied for registry schema validation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: erral

.github/workflows/ci.yml

@@ -52,6 +52,10 @@ jobs:
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13"]
         plone-version: ["6.1-latest", "6.0-latest"]
+        exclude:
+          # Python 3.13 is only supported in Plone 6.1+
+          - python-version: "3.13"
+            plone-version: "6.0-latest"
     with:
       python-version: ${{ matrix.python-version }}
       plone-version: ${{ matrix.plone-version }}