fix: normalize content-type header check for case insensitivity

[tinas]

Summary

This PR addresses an issue where the content-type header check was case-sensitive, causing valid Content-Type values like Text/html to be rejected. The solution normalizes the content-type header using .toLowerCase() to ensure case-insensitive checks.

Reproduction Steps

1. Make a request to a URL with a Content-Type header of Text/html; charset=utf-8.
2. The scraper incorrectly throws an error:

Page must return a header content-type with text/

3. Expected behavior: The scraper should successfully process URLs with case-insensitive Content-Type headers.

Changes Made

• Updated the content-type check in the scraper logic to use toLowerCase().
• Added a new test case for case-insensitive Content-Type values:
  • Content-Type: Text/html now works as expected.
• Verified existing tests to ensure no regressions.

[jshemas]

Thanks for the PR!

[jshemas]

Changes are live in open-graph-scraper@6.8.4