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When running Linux on WSL, Popen.kill() can raise a ProcessLookupError if
the process does not exist anymore, which can happen here since the
previous statement already tries to close the process by sending Ctrl-D to
the running repl.  This doesn't seem to be a problem on other OSes, so just
swallow the exception silently since it indicates the process has been
closed already, which after all is what we want.