wordpress wp-admin/includes/shema.php file has been modify alone

I have a problem, a file from wp-admin has been modified alone or after deactivated/activated my own plugin . I never modified any files inside wp-admin, I don't know why now. I am currently creating a plugin to add some information inside database from a form . After updating a table inside database, i must deactivated and activated the plugin to apply the changes. Also I have to get a backup of one file inside wp-content from my host ! I can't imagine that this process was able to modify a file of wp-admin

Parse error: syntax error, unexpected end of file, expecting ')' in website/wp-admin/includes/schema.php on line 440

after checking, the content of the file is deleted after line 440: 'ping_sites' =

Does anyone have any idea why.