docs: update WebVitals component

[abdonrd]

What?

Update WebVitals component.

Why?

In the useReportWebVitals documentation:
https://nextjs.org/docs/app/api-reference/functions/use-report-web-vitals

If you do it in a TypeScript project, you have this error:

'WebVitals' cannot be used as a JSX component.
  Its type '() => void' is not a valid JSX element type.
    Type '() => void' is not assignable to type '(props: any, deprecatedLegacyContext?: any) => ReactNode'.
      Type 'void' is not assignable to type 'ReactNode'.ts(2786)

How?

Returning null solves the problem.

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 23e5ed8

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 23e5ed8

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: d165d02

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer