fix array spread type bug

compiler/tests/array/spread.leo

@@ -1,6 +1,7 @@
 // A spread operator `...` copies the elements of one array into another
 function main(a: [u8; 3]) {
     let b = [1u8, 1u8];
+    let c = [1u8, ...b];
 
-    console.assert(a == [1u8, ...b]);
+    console.assert(a == c);
 }

type-inference/src/objects/frame.rs

@@ -837,7 +837,7 @@ impl Frame {
 
                 // Check that the type is an array.
                 match array_type {
-                    Type::Array(element_type) => Ok(Type::Array(element_type)),
+                    Type::Array(element_type) => Ok(*element_type),
                     type_ => Err(FrameError::invalid_spread(type_, span)),
                 }
             }