Rollup merge of #109211 - mili-l:mili_l/update_e0206_description, r=WaffleLapkin

E0206 - update description

added `union` to description

Author: matthiaskrgr

compiler/rustc_error_codes/src/error_codes/E0206.md

@@ -1,5 +1,5 @@
-The `Copy` trait was implemented on a type which is neither a struct nor an
-enum.
+The `Copy` trait was implemented on a type which is neither a struct, an
+enum, nor a union.
 
 Erroneous code example:
 
@@ -10,6 +10,6 @@ struct Bar;
 impl Copy for &'static mut Bar { } // error!
 ```
 
-You can only implement `Copy` for a struct or an enum.
+You can only implement `Copy` for a struct, an enum, or a union.
 The previous example will fail because `&'static mut Bar`
-is not a struct or enum.
+is not a struct, an enum, or a union.