Fix page cache purge

[spiralofhope]

When attempting to perform a page cache clear, e.g. https://blog.spiralofhope.com/?clear-blogtext-cache=true

• WordPress version 6.6
• Current plugin: BlogText for WordPress (version 0.9.10)
• PHP version 8.1.29

An error of type E_ERROR was caused in line 75 of the file /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/api/cache-api.php. Error message: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, string given in /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/api/cache-api.php:75
Stack trace:
#0 /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/api/cache-api.php(75): mysqli_query()
#1 /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/markup/markup_cache.php(154): MSCL_PersistentObjectCache->clear_cache()
#2 /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/markup/blogtext_markup.php(276): MarkupCache->clear_page_cache()
#3 /path/to/blog.spiralofhope.com/wp-content/plugins/blogtext/admin/adminbar.php(61): BlogTextMarkup::clear_page_cache()
#4 /path/to/blog.spiralofhope.com/wp-includes/class-wp-hook.php(324): BlogTextAdminBarMenu->handle_request()
#5 /path/to/blog.spiralofhope.com/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#6 /path/to/blog.spiralofhope.com/wp-includes/plugin.php(517): WP_Hook->do_action()
#7 /path/to/blog.spiralofhope.com/wp-settings.php(700): do_action()
#8 /path/to/blog.spiralofhope.com/wp-config.php(108): require_once('/path/to/blog....')
#9 /path/to/blog.spiralofhope.com/wp-load.php(50): require_once('/path/to/blog....')
#10 /path/to/blog.spiralofhope.com/wp-admin/admin.php(34): require_once('/path/to/blog....')
#11 /path/to/blog.spiralofhope.com/wp-admin/plugins.php(10): require_once('/path/to/blog....')
#12 {main}
  thrown