fix: set ruff target-version to py39 (minimum supported version)

With target-version py314, ruff format applies PEP 758 (parentheses-free
except clauses), which is invalid syntax on Python < 3.14. Since the
project supports Python 3.9+, the target must match the minimum version
to prevent incompatible syntax in formatted code.

Author: fgmacedo

AGENTS.md

@@ -72,7 +72,7 @@ uv run mypy statemachine/ tests/
 
 ## Code style
 
-- **Formatter/Linter:** ruff (line length 99, target Python 3.14)
+- **Formatter/Linter:** ruff (line length 99, target Python 3.9)
 - **Rules:** pycodestyle, pyflakes, isort, pyupgrade, flake8-comprehensions, flake8-bugbear, flake8-pytest-style
 - **Imports:** single-line, sorted by isort
 - **Docstrings:** Google convention

pyproject.toml

@@ -134,7 +134,7 @@ ignore_missing_imports = true
 src = ["statemachine"]
 
 line-length = 99
-target-version = "py314"
+target-version = "py39"
 
 # Exclude a variety of commonly ignored directories.
 exclude = [