py(deps[testing,lint]) Add typing-extensions for older python versions (#564)

Follow up to #562

Author: tony

CHANGES

@@ -20,6 +20,11 @@ $ pip install --user --upgrade --pre libtmux
 - tests: Import `Self` in a `TYPE_CHECKING` guard to prevent dependency issues.
   Via #562, Thank you @ppentchev!
 
+### Development
+
+- dev dependencies: Include `typing-extensions` for Python version < 3.11 via
+  the `testing` and `lint` groups, via #564.
+
 ## libtmux 0.42.0 (2025-02-02)
 
 ### Bug fixes

pyproject.toml

@@ -64,6 +64,7 @@ dev-dependencies = [
   "myst-parser",
   "linkify-it-py",
   # Testing
+  "typing-extensions; python_version < '3.11'",
   "gp-libs",
   "pytest",
   "pytest-rerunfailures",
@@ -94,6 +95,7 @@ docs = [
   "linkify-it-py",
 ]
 testing = [
+  "typing-extensions; python_version < '3.11'",
   "gp-libs",
   "pytest",
   "pytest-rerunfailures",
@@ -106,6 +108,7 @@ coverage =[
   "pytest-cov",
 ]
 lint = [
+  "typing-extensions; python_version < '3.11'",
   "ruff",
   "mypy",
 ]