IGNFrance tests: fix `exactly_one` warning
IGNFrance tests: fix `exactly_one` warning

test/geocoders/ignfrance.py::IGNFranceTestCase::test_reverse_no_result
  <...>/geopy/test/geocoders/util.py:91: DeprecationWarning: IGNFrance.reverse: default value for `exactly_one` argument will become True in geopy 2.0. Specify `exactly_one=False` as the argument explicitly to get rid of this warning.

jmb/geopy,geopy/geopy