Change diff file path in Webpack guide

[julien-deramond]

Description

This PR contains a small fix to use the same reference for the diff in the Webpack guide.
When we follow the tutorial, we are in the my-project directory, so when we are doing the diffs, it is in this directory and not in a webpack directory (as in twbs/examples).

There are no diffs in Parcel and Vite guides so this is the only place where a modification is needed.

Motivation & Context

Consistency between diffs in this guide.

Type of changes

• Enhancement (non-breaking change)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• (N/A) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-38339--twbs-bootstrap.netlify.app/docs/5.3/getting-started/webpack/#extracting-css
• https://deploy-preview-38339--twbs-bootstrap.netlify.app/docs/5.3/getting-started/webpack/#extracting-svg-files