Fix CI for Rust 1.61.0 (#4164)

A new version of rustc was released this morning and we have a few small
breakages on our CI which need fixing:

* A new warning was coming out of the c-api crate about an unneeded
  `unsafe` block.
* The panic message of a task in `cranelift-object` needed updating
  since the standard library changed how it formats strings with the nul
  byte.

crates/c-api/src/func.rs

@@ -265,7 +265,7 @@ pub(crate) unsafe fn c_callback_to_rust_fn(
 
         // Translate the `wasmtime_val_t` results into the `results` space
         for (i, result) in out_results.iter().enumerate() {
-            results[i] = unsafe { result.to_val() };
+            results[i] = result.to_val();
         }
 
         // Move our `vals` storage back into the store now that we no longer