fix: Change sideEffects value to boolean

[filipechagas]

As described in Webpack documentation, this field is boolean or string[]

Check https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free

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Fixes https://github.com/googleapis/google-api-nodejs-client/issues/3419 🦕

[filipechagas]

I see there's already a PR for that https://github.com/googleapis/google-api-nodejs-client/pull/3428#pullrequestreview-1885578244