[CI] Use Python 3.14 for regression tests (#14973)

Author: srittau

.github/workflows/tests.yml

@@ -75,9 +75,7 @@ jobs:
       - uses: actions/checkout@v5
       - uses: actions/setup-python@v6
         with:
-          # Use py311 for now, as py312 seems to be around 30s slower in CI
-          # TODO: figure out why that is (#11590)
-          python-version: "3.11"
+          python-version: "3.14"
       - uses: astral-sh/setup-uv@v6
         with:
           version-file: "requirements-tests.txt"