Kinsta opcache error fix

### Explanation
The error:

Fatal error: Uncaught Error: Call to undefined function Kinstaopcache_reset()

suggests that the Kinsta plugin is trying to use the PHP `opcache_reset()` function, which is used to clear the PHP OPcache. This function may not be available if:
1. **The OPcache extension is not installed** on your server.
2. **OPcache is installed but not enabled** in your PHP configuration.
3. You're using an older version of PHP that doesn't support OPcache (although it's available in PHP versions 5.5+).

### Solutions

#### 1. Ensure OPcache is installed and enabled
You need to verify if OPcache is installed and enabled on your server.

– Create a new PHP file (e.g., `phpinfo.php`) with the following content:

<?php phpinfo(); ?>

– Access this file in your browser (e.g., `https://yourdomain.com/phpinfo.php`).
– Look for a section called `Zend OPcache`. If it's not there, OPcache is not installed.

If you're managing your own server (not using managed hosting like Kinsta):
– Open your `php.ini` file and ensure you have the following lines:

[opcache]
  zend_extension=opcache
  opcache.enable=1

– Restart your web server after making changes.

#### 2. Disable the Kinsta MU plugin temporarily
If you need a quick fix and you're unable to enable OPcache, you can temporarily disable the Kinsta MU plugin:

– Access your site via FTP or a file manager.
– Navigate to `web/app/mu-plugins/kinsta-mu-plugins/`.
– Rename the `kinsta-mu-plugins` folder to something like `kinsta-mu-plugins-disabled`.

**Note**: This might affect some caching and performance optimizations provided by Kinsta, so use this as a temporary solution.

#### 3. Contact Kinsta Support
If your site is hosted on Kinsta, the best approach would be to reach out to their support team. They can adjust the server settings for you or guide you through the steps to enable OPcache properly.

#### 4. Add a check before calling `opcache_reset()`
If you're comfortable editing code, you can modify the Kinsta plugin file to check if the function exists before calling it. Edit `class-cache-purge.php` (around line 260) and wrap the call like this:

if (function_exists('opcache_reset')) {
    opcache_reset();
}

This will prevent the error if `opcache_reset()` is unavailable. However, be cautious with this approach as it may be overwritten by plugin updates.