pythonPackages.cryptography: fix test on macOS 10.12

Hydra didn't notice because it's running 10.11.

pkgs/top-level/python-packages.nix

@@ -4526,6 +4526,14 @@ in {
     propagatedBuildInputs = with self; [ six idna ipaddress pyasn1 cffi pyasn1-modules pytz ]
      ++ optional (pythonOlder "3.4") self.enum34;
 
+    # The test assumes that if we're on Sierra or higher, that we use `getentropy`, but for binary
+    # compatibility with pre-Sierra for binary caches, we hide that symbol so the library doesn't
+    # use it. This boils down to them checking compatibility with `getentropy` in two different places,
+    # so let's neuter the second test.
+    patchPhase = ''
+      substituteInPlace ./tests/hazmat/backends/test_openssl.py --replace '"16.0"' '"99.0"'
+    '';
+
     # IOKit's dependencies are inconsistent between OSX versions, so this is the best we
     # can do until nix 1.11's release
     __impureHostDeps = [ "/usr/lib" ];