Correct the documentation comment for field_config_update_validate()

[kiamlaluno]

In the field.module file, field_config_update_validate() has the following documentation comment.

/**
 * Implements hook_config_create_update().
 */

Since hook_config_create_update() is not a documented hook, field_config_update_validate() must be a hook_config_update_validate() implementation.

[kiamlaluno]

(I apologize: At 8:30 PM, I probably had hallucinations when I was watching the code.)

[argiepiano]

RTBC

[quicksketch]

Thanks @kiamlaluno and @argiepiano! Merged backdrop/backdrop#4593 into 1.x and 1.26.x.