Type-check with mypy on Python 3.10

mypy took the interpreter's version, so CI on Python 3.12 checked a branch of the runtime that pyright, set to 3.10, never sees.

Signed-off-by: Shrijayan <81805145+shrijayan@users.noreply.github.com>

Author: shrijayan

pyproject.toml

@@ -150,6 +150,8 @@ reportUnknownParameterType = false
 reportUnusedFunction = false
 
 [tool.mypy]
+# Checked on the lowest supported Python, as pyright is (pythonVersion).
+python_version = "3.10"
 pretty = true
 show_error_codes = true