build.yml: bump the python-version to 3.11

as per @fruch,

> we are using our own python version from scylla-python3, and currently
> on master it's 3.11

so, let's test with the version we use in production. this should
also unlock the features from the language and the standard library
provided in higher versions of CPython.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

.github/workflows/build.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@v3
         with:
-          python-version: 3.8                         
+          python-version: 3.11
           architecture: x64
 
       - name: unittest