Pin to pyo3 470716e

This revision of pyo3 contains a fix for PyO3/pyo3#1264.

Author: marco-c

Cargo.lock

@@ -14,7 +14,8 @@ crate-type = ["cdylib"]
 parsepatch = "0.2"
 
 [dependencies.pyo3]
-version = "0.12"
+git = "https://github.com/Pyo3/pyo3.git"
+rev = "470716e"
 features = ["extension-module"]
 
 [package.metadata.maturin]