Use Python 3.10 for pytestmain job

pytest's main has since then dropped support for Python 3.9, so the job that runs with pytest's main needs to run in Python 3.10 now.

Author: nicoddemus

.github/workflows/main.yml

@@ -33,7 +33,7 @@ jobs:
           "windows-py313",
           "windows-pypy3",
 
-          "ubuntu-py39-pytestmain",
+          "ubuntu-py310-pytestmain",
           "ubuntu-py39",
           "ubuntu-py310",
           "ubuntu-py311",
@@ -56,10 +56,10 @@ jobs:
             python: "pypy3.9"
             os: windows-latest
             tox_env: "pypy3"
-          - name: "ubuntu-py39-pytestmain"
-            python: "3.9"
+          - name: "ubuntu-py310-pytestmain"
+            python: "3.10"
             os: ubuntu-latest
-            tox_env: "py39-pytestmain"
+            tox_env: "py310-pytestmain"
             use_coverage: true
           - name: "ubuntu-py39"
             python: "3.9"