Add test for bad cast with deferred projection equality

tests/ui/typeck/lazy-norm/cast-checks-handling-projections.rs

@@ -0,0 +1,6 @@
+// compile-flags: -Ztrait-solver=next
+// known-bug: unknown
+
+fn main() {
+    (0u8 + 0u8) as char;
+}

tests/ui/typeck/lazy-norm/cast-checks-handling-projections.stderr

@@ -0,0 +1,9 @@
+error[E0271]: type mismatch resolving `char == <u8 as Add>::Output`
+  --> $DIR/cast-checks-handling-projections.rs:5:5
+   |
+LL |     (0u8 + 0u8) as char;
+   |     ^^^^^^^^^^^ types differ
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0271`.