ci: Add missing macOS CI envs (pytest-dev#9601)

alinsa_vix in Discord noticed that we are not testing Python 3.9 and 3.10 on macOS, which seems strange. Maybe this is due how to macOS CI resources were quite scarce for a while, but I believe this has improved since.

.github/workflows/main.yml

@@ -48,6 +48,8 @@ jobs:
 
           "macos-py37",
           "macos-py38",
+          "macos-py39",
+          "macos-py310",
 
           "docs",
           "doctesting",
@@ -116,6 +118,14 @@ jobs:
             os: macos-latest
             tox_env: "py38-xdist"
             use_coverage: true
+          - name: "macos-py39"
+            python: "3.9"
+            os: macos-latest
+            tox_env: "py39-xdist"
+          - name: "macos-py310"
+            python: "3.10"
+            os: macos-latest
+            tox_env: "py310-xdist"
 
           - name: "plugins"
             python: "3.9"