Fix: Escaped shortcodes are no longer expanded in get_the_excerpt()

[kashviyadav09]

Trac Ticket: https://core.trac.wordpress.org/ticket/12345

### Description
This pull request fixes an issue where escaped shortcodes were being expanded in get_the_excerpt().

Previously, shortcodes wrapped in escaping functions (like \[shortcode]) were still processed and rendered, which is not the expected behavior. With this patch, escaped shortcodes are preserved as plain text in excerpts, ensuring consistency and preventing unexpected content output.

### Changes Made

• Updated get_the_excerpt() logic to respect escaped shortcodes
• Added automated PHPUnit tests to cover this scenario
• Ensured backward compatibility with existing excerpts

### Testing

• Added tests in tests/phpunit/tests/shortcodes/ to verify escaped shortcodes remain unexpanded
• Run PHPUnit to confirm all tests pass: