Add Python 3.13 to CI.

Author: anntzer

.github/workflows/build.yml

@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, macos-11, windows-2019]
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v3