Corrected expected test err messages.

Author: Alexander Regueiro

src/test/ui/issues/issue-56199.rs

@@ -5,18 +5,18 @@ struct Bar {}
 impl Foo {
     fn foo() {
         let _ = Self;
-        //~^ ERROR the `Self` constructor can only be used with tuple structs
+        //~^ ERROR the `Self` constructor can only be used with tuple or unit structs
         let _ = Self();
-        //~^ ERROR the `Self` constructor can only be used with tuple structs
+        //~^ ERROR the `Self` constructor can only be used with tuple or unit structs
     }
 }
 
 impl Bar {
     fn bar() {
         let _ = Self;
-        //~^ ERROR the `Self` constructor can only be used with tuple structs
+        //~^ ERROR the `Self` constructor can only be used with tuple or unit structs
         let _ = Self();
-        //~^ ERROR the `Self` constructor can only be used with tuple structs
+        //~^ ERROR the `Self` constructor can only be used with tuple or unit structs
     }
 }
 

src/test/ui/issues/issue-56199.stderr

@@ -1,26 +1,26 @@
-error: the `Self` constructor can only be used with tuple structs
+error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/issue-56199.rs:7:17
    |
 LL |         let _ = Self;
    |                 ^^^^
    |
    = note: did you mean to use one of the enum's variants?
 
-error: the `Self` constructor can only be used with tuple structs
+error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/issue-56199.rs:9:17
    |
 LL |         let _ = Self();
    |                 ^^^^
    |
    = note: did you mean to use one of the enum's variants?
 
-error: the `Self` constructor can only be used with tuple structs
+error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/issue-56199.rs:16:17
    |
 LL |         let _ = Self;
    |                 ^^^^ did you mean `Self { /* fields */ }`?
 
-error: the `Self` constructor can only be used with tuple structs
+error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/issue-56199.rs:18:17
    |
 LL |         let _ = Self();

src/test/ui/issues/issue-56835.rs

@@ -3,7 +3,7 @@ pub struct Foo {}
 
 impl Foo {
     fn bar(Self(foo): Self) {}
-    //~^ ERROR the `Self` constructor can only be used with tuple structs
+    //~^ ERROR the `Self` constructor can only be used with tuple or unit structs
     //~^^ ERROR expected tuple struct/variant, found self constructor `Self` [E0164]
 }
 

src/test/ui/issues/issue-56835.stderr

@@ -1,4 +1,4 @@
-error: the `Self` constructor can only be used with tuple structs
+error: the `Self` constructor can only be used with tuple or unit structs
   --> $DIR/issue-56835.rs:5:12
    |
 LL |     fn bar(Self(foo): Self) {}