Python 3.7 is not supported.

Assignement expression[*] is new in python 3.8
And python 3.7 is already end of life.

Also add testing on 3.12.

[*]https://docs.python.org/3/whatsnew/3.8.html#assignment-expressions

.github/workflows/ci.yaml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       max-parallel: 3
       matrix:
-        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
 
     steps:
       - name: checkout