docs: fix README incorrect Chromium skip env variable

[Zacama]

Description

• Updated the README.md to fix an incorrect environment variable (PUPPETEER_SKIP_CHROMIUM_DOWNLOAD) under the Puppeteer setup section.
• Replaced it with the correct variable, PUPPETEER_SKIP_DOWNLOAD, according to the latest Puppeteer documentation (puppeteer.configuration#skipdownload).
• Added a brief note explaining the reasoning for this correction.

Related issue(s)
Fixes #794

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity 😴

It will be closed in 120 days if no further activity occurs. To unstale this pull request, add a comment with detailed explanation.

There can be many reasons why some specific pull request has no activity. The most probable cause is lack of time, not lack of interest. AsyncAPI Initiative is a Linux Foundation project not owned by a single for-profit company. It is a community-driven initiative ruled under open governance model.

Let us figure out together how to push this pull request forward. Connect with us through one of many communication channels we established here.

Thank you for your patience ❤️