rust: fix compilation on 1.32.0

`&self.some_string` apparently didn't `impl Into<String>` until then?

src/git.rs

@@ -151,7 +151,8 @@ impl Identity {
 
 impl Clone for Identity {
     fn clone(&self) -> Self {
-        Self::new(&self.name, &self.email)
+        // XXX(1.36.0): These can be `&self.<field>` in 1.36.0.
+        Self::new(self.name.clone(), self.email.clone())
     }
 }