Bump PyPy version used for CI tests

This should address flakiness related to the PyPy test runners that
would sometimes crash on startup.

The underlying issue was tracked down by Carl Friedrich Bolz-Tereick and
is explained here: https://www.pypy.org/posts/2024/03/fixing-bug-incremental-gc.html

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ['ubuntu-latest', 'windows-2022', 'macos-13']
-        python: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13.0-alpha.3', 'pypy3.9-v7.3.15', 'pypy3.10-v7.3.15']
+        python: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13.0-alpha.3', 'pypy3.9-v7.3.16', 'pypy3.10-v7.3.16']
 
     name: "Python ${{ matrix.python }} / ${{ matrix.os }}"
     runs-on: ${{ matrix.os }}