matrix-synapse: add openssl to buildInputs

It should be included regardless of whether tests are run or not, and
overriding the package to disable tests would break this package up
until this change.

pkgs/servers/matrix-synapse/default.nix

@@ -24,6 +24,8 @@ buildPythonApplication rec {
     ./homeserver-script.patch
   ];
 
+  buildInputs = [ openssl ];
+
   propagatedBuildInputs = [
     setuptools
     bcrypt