fix(dynamic-import-vars): simplify regex

[bluwy]

Rollup Plugin Name: dynamic-import-vars

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

n/a

Description

It looks like we can remove the unneeded [] for the regex as it contains only the \w. I discovered this while running eslint-plugin-regexp:

/Users/bjorn/Work/oss/vite/node_modules/.pnpm/@rollup+plugin-dynamic-import-vars@2.1.2_rollup@4.18.1/node_modules/@rollup/plugin-dynamic-import-vars/dist/cjs/index.js
  117:47  error  Unexpected character class with one character class escape. Can remove brackets  regexp/no-useless-character-class

It's not a significant change and unlikely to affect perf, but should help with readability.