🧪 Add a MyPy check against Python 3.10

This is an intermediate version between 3.8 and 3.12 which should give
a good overall idea of how well the project is type-covered across the
supported version range even with 3.9 and 3.11 being excluded.

.pre-commit-config.yaml

@@ -137,6 +137,21 @@ repos:
     - --txt-report=.tox/.tmp/.mypy/python-3.8
     - cheroot/
     pass_filenames: false
+  - id: mypy
+    alias: mypy-py310
+    name: MyPy, for Python 3.10
+    additional_dependencies:
+    - lxml
+    - types-backports
+    - types-pyOpenSSL
+    - types-requests
+    args:
+    - --install-types
+    - --non-interactive
+    - --python-version=3.10
+    - --txt-report=.tox/.tmp/.mypy/python-3.10
+    - cheroot/
+    pass_filenames: false
   - id: mypy
     alias: mypy-py312
     name: MyPy, for Python 3.12