Add regression test

Author: SkiFire13

src/test/ui/cast/issue-84213.fixed

@@ -0,0 +1,15 @@
+// run-rustfix
+
+struct Something {
+    pub field: u32,
+}
+
+fn main() {
+    let mut something = Something { field: 1337 };
+
+    let _pointer_to_something = &something as *const Something;
+    //~^ ERROR: non-primitive cast
+
+    let _mut_pointer_to_something = &mut something as *mut Something;
+    //~^ ERROR: non-primitive cast
+}

src/test/ui/cast/issue-84213.rs

@@ -0,0 +1,15 @@
+// run-rustfix
+
+struct Something {
+    pub field: u32,
+}
+
+fn main() {
+    let mut something = Something { field: 1337 };
+
+    let _pointer_to_something = something as *const Something;
+    //~^ ERROR: non-primitive cast
+
+    let _mut_pointer_to_something = something as *mut Something;
+    //~^ ERROR: non-primitive cast
+}

src/test/ui/cast/issue-84213.stderr

@@ -0,0 +1,25 @@
+error[E0605]: non-primitive cast: `Something` as `*const Something`
+  --> $DIR/issue-84213.rs:10:33
+   |
+LL |     let _pointer_to_something = something as *const Something;
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+help: borrow the value for the cast to be valid
+   |
+LL |     let _pointer_to_something = &something as *const Something;
+   |                                 ^
+
+error[E0605]: non-primitive cast: `Something` as `*mut Something`
+  --> $DIR/issue-84213.rs:13:37
+   |
+LL |     let _mut_pointer_to_something = something as *mut Something;
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid cast
+   |
+help: borrow the value for the cast to be valid
+   |
+LL |     let _mut_pointer_to_something = &mut something as *mut Something;
+   |                                     ^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0605`.