chore: Pin Renovate-allowed Python to <3.12 in workflows

dbt-common's pinned mashumaro raises UnserializableField on Python 3.14
at import time. The upstream cloudquery preset has allowedVersions: "<3.14",
which didn't block this PR's 3.11 -> 3.14 bump for unclear reasons; tighten
locally to <3.12 scoped to the github-actions manager so the python-version
in setup-python stays on the 3.11 series.

Author: erezrokah

.github/renovate.json5

@@ -18,5 +18,10 @@
         '/^dbt-/',
       ],
     },
+    {
+      matchManagers: ['github-actions'],
+      matchPackageNames: ['python'],
+      allowedVersions: '<3.12',
+    },
   ],
 }