Update puffin to 0.18 (#3600)

THe profiling macros now contain unsafe code (but in a safe way), so
`#[foribd(unsafe)]` had to become `#[deny(unsafe)]`

crates/egui/src/lib.rs

@@ -336,7 +336,7 @@
 
 #![allow(clippy::float_cmp)]
 #![allow(clippy::manual_range_contains)]
-#![forbid(unsafe_code)]
+#![deny(unsafe_code)]
 
 mod animation_manager;
 pub mod containers;