move crosspointer_transmute from complexity to suspicious (#15403)

changelog: [`crosspointer_transmute`]: move from `complexity` to
`suspicious`

this looks to me like an obvious miscategorisation -- and there was
already [a proposal to move the
lint](#6626 (comment))

Author: samueltardieu

clippy_lints/src/transmute/mod.rs

@@ -105,7 +105,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub CROSSPOINTER_TRANSMUTE,
-    complexity,
+    suspicious,
     "transmutes that have to or from types that are a pointer to the other"
 }