plugabble function check_admin_referer() not pluggable?

Hello,

I would like to override the mentionned function. I created a file to do that and put it in the plugins folder.
When activating the plugin I get this error:
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Fatal error: Cannot redeclare check_admin_referer() (previously declared in /home/isbi/www/wp-includes/pluggable.php:1087) in /home/patati/www/wp-content/plugins/my_plugin.php on line 42
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I thought that if the function is in plugin, the core function wasn’t loaded. Here the reference where I found this info: https://codex.wordpress.org/Pluggable_Functions
If I add the if( ! function_exists(‘check_admin_referer’) ){} test, my custom function won’t be loaded.

Thanks in advance for your reply.