Unpin Python version for builds (#151)

Follow-up after python/cpython#146623 is released.

Author: m-aciek

.github/workflows/update-and-build.yml

@@ -83,7 +83,7 @@ jobs:
     steps:
       - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97  # v7.0.0
         with:
-          python-version: 3.12  # pin for Sphinx 3.4.3 in 3.10 branch (see  # 63)
+          python-version: 3
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
         with:
           repository: python/cpython