or-tools: disable parallel-building

protobuf generation is not thread safe

```
       > ./ortools/scheduling/rcpsp_parser.h:24:10: fatal error: ortools/scheduling/rcpsp.pb.h: No such file or directory
       >    24 | #include "ortools/scheduling/rcpsp.pb.h"
```

pkgs/development/libraries/science/math/or-tools/default.nix

@@ -77,7 +77,8 @@ stdenv.mkDerivation rec {
     (cd temp_python/ortools; PYTHONPATH="$python/${python.sitePackages}:$PYTHONPATH" python setup.py install '--prefix=$python')
   '';
 
-  enableParallelBuilding = true;
+  # protobuf generation is not thread safe
+  enableParallelBuilding = false;
 
   nativeBuildInputs = [
     cmake