Modify primary span label for E0308

The previous output was unintuitive to users.

tests/ui/array-slice-vec/array-not-vector.rs

@@ -1,12 +1,12 @@
 fn main() {
     let _x: i32 = [1, 2, 3];
     //~^ ERROR mismatched types
-    //~| expected `i32`, found array
+    //~| expected `i32`, found `[{integer}; 3]`
 
     let x: &[i32] = &[1, 2, 3];
     let _y: &i32 = x;
     //~^ ERROR mismatched types
     //~| expected reference `&i32`
     //~| found reference `&[i32]`
-    //~| expected `i32`, found slice
+    //~| expected `&i32`, found `&[i32]`
 }

tests/ui/array-slice-vec/array-not-vector.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/array-not-vector.rs:2:19
    |
 LL |     let _x: i32 = [1, 2, 3];
-   |             ---   ^^^^^^^^^ expected `i32`, found array `[{integer}; 3]`
+   |             ---   ^^^^^^^^^ expected `i32`, found `[{integer}; 3]`
    |             |
    |             expected due to this
 
@@ -10,7 +10,7 @@ error[E0308]: mismatched types
   --> $DIR/array-not-vector.rs:7:20
    |
 LL |     let _y: &i32 = x;
-   |             ----   ^ expected `i32`, found slice `[i32]`
+   |             ----   ^ expected `&i32`, found `&[i32]`
    |             |
    |             expected due to this
    |

tests/ui/array-slice-vec/slice-to-vec-comparison.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
   --> $DIR/slice-to-vec-comparison.rs:4:9
    |
 LL |     a > b;
-   |         ^ expected array of 0 elements, found struct `Vec`
+   |         ^ expected `&[_; 0]`, found `&Vec<u8>`
    |
    = note: expected reference `&[_; 0]`
               found reference `&Vec<u8>`