Add regression test for <i32 as Iterator>::count

Fixes #84495

src/test/ui/methods/issues/issue-84495.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let x: i32 = 1;
+    println!("{:?}", x.count()); //~ ERROR is not an iterator
+}

src/test/ui/methods/issues/issue-84495.stderr

@@ -0,0 +1,13 @@
+error[E0599]: `i32` is not an iterator
+  --> $DIR/issue-84495.rs:3:24
+   |
+LL |     println!("{:?}", x.count());
+   |                        ^^^^^ `i32` is not an iterator
+   |
+   = note: the following trait bounds were not satisfied:
+           `i32: Iterator`
+           which is required by `&mut i32: Iterator`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.