Test on Python 3.16-dev (#449)

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 79937b9..47fd400 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -35,6 +35,7 @@
         - "3.13"
         - "3.14"
         - "3.15"
+        - "3.16-dev"
     steps:
     - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
     - name: Set up Python ${{ matrix.python-version }}