Bump WP version requirement to 6.5+

[swissspidy]

Previously:

• Bump WP version requirement to 6.4+ #13703

Field guide: https://make.wordpress.org/core/2024/03/15/wordpress-6-5-field-guide/

Notable changes:

• Interactivity API now available by default, making Use Interactivity API for frontend functionality #13704 easier

Tasks include:

• Bump in readme.txt
• Bump in web-stories.php (twice)
• Update minimum_supported_wp_version in phpcs.xml.dist
• Run e2e tests against 6.5 and newer
• Run unit tests against 6.5 and newer
• Re-evaluate PHPUnit matrix and composer dependencies if necessary

[swissspidy]

The AMP plugin now also requires 6.5, so now we should definitely bump as well.