devel/dtool: Fix build with rust-1.76.0

Import upstream patch [1] to fix the following error:

error[E0310]: the parameter type `T` may not live long enough
    --> /wrkdirs/usr/ports/devel/dtool/work/dtool-0.12.0/cargo-crates/rustc-serialize-0.3.24/src/serialize.rs:1155:5

[1] https://github.com/rust-lang-deprecated/rustc-serialize/commit/75ce92452a5f7c25a58fdea81e5f6f888630a2c9

PR:		276920
Approved by:	portmgr (build fix blanket)