fix: verify commit msg.

When I try to make vue core a submodule of my project：

git submodule add https://github.com/vuejs/core.git

do something and git commit:

git commit -am "docs: add comments."

it will throw error：

➜  core git:(heads/v3.4.21) ✗ git commit -am "docs: add comments."
✔ Preparing lint-staged...
✔ Running tasks for staged files...
✔ Applying modifications from tasks...
✔ Cleaning up temporary files...

> @3.4.21 check /Volumes/work_data/Web_data/Web_project/code/Vue3/source/core
> tsc --incremental --noEmit

node:fs:453
    return binding.readFileUtf8(path, stringToFlags(options.flag));
                   ^

Error: ENOTDIR: not a directory, open '/Volumes/work_data/Web_data/Web_project/code/Vue3/source/core/.git/COMMIT_EDITMSG'
    at readFileSync (node:fs:453:20)
    at file:///Volumes/work_data/Web_data/Web_project/code/Vue3/source/core/scripts/verify-commit.js:7:13
    at ModuleJob.run (node:internal/modules/esm/module_job:218:25)
    at async ModuleLoader.import (node:internal/modules/esm/loader:329:24)
    at async loadESM (node:internal/process/esm_loader:34:7)
    at async handleMainPromise (node:internal/modules/run_main:113:12) {
  errno: -20,
  code: 'ENOTDIR',
  syscall: 'open',
  path: '/Volumes/work_data/Web_data/Web_project/code/Vue3/source/core/.git/COMMIT_EDITMSG'
}

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	90.5 kB	34.4 kB	31 kB
vue.global.prod.js	148 kB	53.7 kB	47.9 kB

Usages

Name	Size	Gzip	Brotli
createApp	50.7 kB	19.8 kB	18.1 kB
createSSRApp	54.1 kB	21.1 kB	19.3 kB
defineCustomElement	53 kB	20.6 kB	18.7 kB
overall	64.4 kB	24.8 kB	22.5 kB

I don't think it's necessary to add this check given our current repository setup. It could create more work for the Vue.js maintainers without providing clear benefits for us. Plus, future maintainers might not even understand the purpose of these lines.

Since you're making Vue a submodule of your project, I believe you can address this in your own repository without needing to merge this change back to the upstream.

Thanks anyway! I learned a lot from this PR.