fix: resolve ruff format and lint errors in tests

Author: Akagi201

tests/test_shellflow.py

@@ -13,13 +13,10 @@
 from typing import Any
 from unittest import mock
 
-import os
 import pytest
 from hypothesis import given
 from hypothesis import strategies as st
 
-ZSH_AVAILABLE = os.path.exists("/bin/zsh")
-
 from shellflow import (
     VALID_EXPORT_SOURCES,
     Block,
@@ -42,6 +39,8 @@
     run_script,
 )
 
+ZSH_AVAILABLE = Path("/bin/zsh").exists()
+
 VALID_EXPORT_NAME_STRATEGY = st.from_regex(r"[A-Za-z_][A-Za-z0-9_]*", fullmatch=True)
 INVALID_EXPORT_NAME_STRATEGY = st.one_of(
     st.from_regex(r"[0-9][A-Za-z0-9_]*", fullmatch=True),