That last mv command should not have a dollar sign in front: it's something make runs. Also the current makefile has a cp command, which is more in the spirit of "make install". So it should be
$ make DEVELOP=1 PREFIX=$PREFIX installcp -vf scrip*.so ../../../pyromsscrip.cpython-37m-x86_64-linux-gnu.so -> ../../../pyroms/scrip.cpython-37m-x86_64-linux-gnu.so
In README.md for the installation of the scrip extension we have
$ make DEVELOP=1 PREFIX=$PREFIX install
$ mv -vf scrip*.so ../../../pyroms
scrip.cpython-37m-x86_64-linux-gnu.so -> ../../../pyroms/scrip.cpython-37m-x86_64-linux-gnu.so
That last mv command should not have a dollar sign in front: it's something make runs. Also the current makefile has a cp command, which is more in the spirit of "make install". So it should be
$ make DEVELOP=1 PREFIX=$PREFIX install
cp -vf scrip*.so ../../../pyroms
scrip.cpython-37m-x86_64-linux-gnu.so -> ../../../pyroms/scrip.cpython-37m-x86_64-linux-gnu.so