Run ubuntu mypyc tests on 3.10 (#20169)

from Emma
#20155 (comment)

Author: hauntsaninja

.github/workflows/test.yml

@@ -85,8 +85,8 @@ jobs:
           toxenv: py
           tox_extra_args: "-n 3 mypyc/test/test_run.py mypyc/test/test_external.py"
 
-        - name: mypyc runtime tests with py313-ubuntu
-          python: '3.13'
+        - name: mypyc runtime tests with py310-ubuntu
+          python: '3.10'
           os: ubuntu-latest
           toxenv: py
           tox_extra_args: "-n 3 mypyc/test/test_run.py mypyc/test/test_external.py"