fix(pre-commit): exclude tests from mdformat

tests 目录下文件是测试输入/输出，不应被 mdformat 处理。\n\nAuthored by OpenClaw (model: custom-chat-jinzhezeng-group/gpt-5.3-codex)

Author: njzjz-bot

.pre-commit-config.yaml

@@ -44,6 +44,7 @@ repos:
     rev: 1.0.0
     hooks:
     -   id: mdformat
+        exclude: "^tests/.*$"
         additional_dependencies:
         # - mdformat-myst==0.3.0
         # See https://github.com/executablebooks/mdformat-myst/issues/13