Fix: Version field not updated

[t-hamano]

I noticed that the version field was not taken into account in the sanitize_theme_data method, so we couldn't update this field.

This PR should also resolve the following PHP error that is logged when updating metadata.

PHP Warning:  Undefined array key "version" in /var/www/html/wp-content/plugins/create-block-theme/admin/create-theme/theme-styles.php on line 20

Testing Instructions

• Opne the Edit Theme Metadata modal.
• Update "Version" field.
• Open style.css in your active theme and check the Version: header data.

[pbking]

I've fixed the same in this PR which also fixes some other values that get clobbered.