Bump pypa/cibuildwheel from 2.20.0 to 2.21.0 (#72)

Author: dependabot[bot]

.github/workflows/pythonpackage.yml

@@ -286,7 +286,7 @@ jobs:
           platforms: all
 
       - name: Build wheels
-        uses: pypa/cibuildwheel@v2.20.0
+        uses: pypa/cibuildwheel@v2.21.0
         env:
           # configure cibuildwheel to build native archs ('auto'), and some
           # emulated ones