DO NOT MERGE: Test with memoffset/unstable_offset_of feature

Testing as part of rust-lang/rust#111839

Author: joshlf

Diff for: Cargo.toml

@@ -18,7 +18,7 @@ rust-version = "1.56"
 cfg-if = "1.0"
 libc = "0.2.62"
 parking_lot = ">= 0.11, < 0.13"
-memoffset = "0.9"
+memoffset = { version = "0.9", features = ["unstable_offset_of"] }
 
 # ffi bindings to the python interpreter, split into a separate crate so they can be used independently
 pyo3-ffi = { path = "pyo3-ffi", version = "=0.20.0" }