test: switch to pypy3.11-nightly

Author: nedbat

.github/workflows/python-nightly.yml

@@ -63,7 +63,7 @@ jobs:
           - "3.13"
           - "3.14"
           # https://github.com/actions/setup-python#available-versions-of-pypy
-          - "pypy-3.10"
+          - "pypy-3.11"
         nogil:
           - false
           - true