Fix grammar in actions.variables.id_not_exist (en-US) (#28680)

Fixes the capitalization and grammar of the key.

Author: wackbyte

options/locale/locale_en-US.ini

@@ -3552,7 +3552,7 @@ variables.none = There are no variables yet.
 variables.deletion = Remove variable
 variables.deletion.description = Removing a variable is permanent and cannot be undone. Continue?
 variables.description = Variables will be passed to certain actions and cannot be read otherwise.
-variables.id_not_exist = Variable with id %d not exists.
+variables.id_not_exist = Variable with ID %d does not exist.
 variables.edit = Edit Variable
 variables.deletion.failed = Failed to remove variable.
 variables.deletion.success = The variable has been removed.