fix: @vite/client http request is 404 not found

[ygj6]

Description

fix issue #4174 (comment)

PR #4061 changed @vite/client to .mjs suffix

vite/packages/vite/src/node/constants.ts

Line 44 in d377aae

export const CLIENT_ENTRY = require.resolve('vite/dist/client/client.mjs')

If resolve.extensions is set, the vite will not ignore .mjs by default.

vite/packages/vite/src/node/plugins/resolve.ts

Lines 295 to 308 in d377aae

	for (const ext of options.extensions || DEFAULT_EXTENSIONS) {
	if (
	(res = tryResolveFile(
	file + ext,
	postfix,
	options,
	false,
	targetWeb,
	options.tryPrefix
	))
	) {
	return res
	}
	}

So @vite/client cannot find the file

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[ygj6]

@sodatea help review, thank you