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/epaint/src/lib.rs

@@ -22,7 +22,7 @@
 
 #![allow(clippy::float_cmp)]
 #![allow(clippy::manual_range_contains)]
-#![forbid(unsafe_code)]
+#![deny(unsafe_code)]
 
 mod bezier;
 pub mod image;