LINT_PATHS in `noxfile.py` doesn't include `vertexai`

It looks like the relatively new vertexai source folder is missing from `LINT_PATHS`. As a consequence it's not linted properly automatically and the codebase has now some lint errors. Suggestion is to update the `LINT_PATHS` variable and fix the formatting for `vertexai/language_models/_distillation.py` and `vertexai/vision_models/_vision_models.py`. This should be a trivial fix.

检查 noxfile.py 中的 LINT_PATHS，然后查看 vertexai/language_models/_distillation.py 和 vertexai/vision_models/_vision_models.py 的格式。更新 lint 路径并格式化这两个指定文件；完成的标准是 vertexai 源代码已纳入自动 lint，并且已修复报告的 lint 错误。

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