fix: correct PHP capitalization in index

[syedahmedx3]

What does this PR do?

Improve repo

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Description

Fixed two formatting/text issues in books/free-programming-books-hi.md:

• Corrected Php → PHP in the table of contents index for consistency with the section heading.

Why is this valuable (or not)?

How do we know it's really free?

For book lists, is it a book? For course lists, is it a course? etc.

Checklist:

• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!

[eshellman]

no changes