Fix test for multiline span ui display

The compiler output changed in such a way that this test was no longer testing what it was meant to.

Author: estebank

tests/ui/codemap_tests/huge_multispan_highlight.rs

@@ -1,5 +1,6 @@
 fn main() {
-    let x = "foo";
+    let _ = match true {
+        true => (
 
 
 
@@ -87,5 +88,30 @@ fn main() {
 
 
 
-    let y = &mut x; //~ ERROR cannot borrow
+
+        ),
+        false => "
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        
+        ", //~^^^^^^^^^^^^^^^^^^^^^^ ERROR `match` arms have incompatible types
+    };
 }

tests/ui/codemap_tests/huge_multispan_highlight.stderr

@@ -1,14 +1,27 @@
-error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable
-  --> $DIR/huge_multispan_highlight.rs:90:13
+error[E0308]: `match` arms have incompatible types
+  --> $DIR/huge_multispan_highlight.rs:93:18
    |
-LL |     let y = &mut x;
-   |             ^^^^^^ cannot borrow as mutable
-   |
-help: consider changing this to be mutable
-   |
-LL |     let mut x = "foo";
-   |         +++
+LL |       let _ = match true {
+   |               ---------- `match` arms have incompatible types
+LL |           true => (
+   |  _________________-
+LL | |
+LL | |
+LL | |
+...  |
+LL | |
+LL | |         ),
+   | |_________- this is found to be of type `()`
+LL |           false => "
+   |  __________________^
+LL | |         
+LL | |         
+LL | |         
+...  |
+LL | |         
+LL | |         ",
+   | |_________^ expected `()`, found `&str`
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0596`.
+For more information about this error, try `rustc --explain E0308`.