`nvm install` passed the progress setting to `nvm_install_binary` and `nvm_install_source` as a prefix assignment,
which bash 3.2 in POSIX mode (macOS's `sh`) keeps after a function call returns,
so one install left `NVM_NO_PROGRESS=0` set,
and every later `nvm install --no-progress` was ignored.
Set it as a local instead.