add py3.7 test

[cunla]

Address #341

[github-actions]

Coverage report:

Name                                                    Stmts   Miss Branch BrPart  Cover
-----------------------------------------------------------------------------------------
fakeredis/__init__.py                                      22      5      2      1    75%
fakeredis/_basefakesocket.py                              252     10    106     10    94%
fakeredis/_command_args_parsing.py                         71      2     42      2    96%
fakeredis/_commands.py                                    359     12    140      8    96%
fakeredis/_connection.py                                   95     10     32      7    87%
fakeredis/_fakesocket.py                                   10      0      0      0   100%
fakeredis/_helpers.py                                     170      5     65      4    96%
fakeredis/_msgs.py                                        101      0      0      0   100%
fakeredis/_server.py                                       60      5     18      3    90%
fakeredis/_tcp_server.py                                   95     14     40     12    79%
fakeredis/_valkey.py                                       36     16     10      1    59%
fakeredis/aioredis.py                                     150     14     47      8    88%
fakeredis/commands_mixins/__init__.py                      21      5      0      0    76%
fakeredis/commands_mixins/bitmap_mixin.py                 200      4    116      2    98%
fakeredis/commands_mixins/connection_mixin.py              33      1     14      1    96%
fakeredis/commands_mixins/generic_mixin.py                268     56    152     12    78%
fakeredis/commands_mixins/geo_mixin.py                    148     11     77      5    90%
fakeredis/commands_mixins/hash_mixin.py                   203      8    106      6    95%
fakeredis/commands_mixins/list_mixin.py                   245      8    152      9    96%
fakeredis/commands_mixins/pubsub_mixin.py                 119      7     66      8    90%
fakeredis/commands_mixins/scripting_mixin.py              175      7     86      7    95%
fakeredis/commands_mixins/server_mixin.py                  89      6     48      4    93%
fakeredis/commands_mixins/set_mixin.py                    144     12     92      6    91%
fakeredis/commands_mixins/sortedset_mixin.py              420     16    225     16    95%
fakeredis/commands_mixins/streams_mixin.py                258     27    160     28    87%
fakeredis/commands_mixins/string_mixin.py                 235      8    147      9    96%
fakeredis/commands_mixins/transactions_mixin.py            74      3     30      2    95%
fakeredis/geo/__init__.py                                   3      0      0      0   100%
fakeredis/geo/geohash.py                                   45      0     18      0   100%
fakeredis/geo/haversine.py                                 10      0      0      0   100%
fakeredis/model/__init__.py                                 5      0      0      0   100%
fakeredis/model/_stream.py                                325     14    122     11    94%
fakeredis/model/_timeseries_model.py                      173     13     84      4    90%
fakeredis/model/_topk.py                                   85      1     30      3    97%
fakeredis/model/_zset.py                                   68      0     16      0   100%
fakeredis/server_specific_commands/__init__.py              2      0      0      0   100%
fakeredis/server_specific_commands/dragonfly_mixin.py      15      7      2      0    59%
fakeredis/stack/__init__.py                                27     14      4      0    42%
fakeredis/stack/_bf_mixin.py                              122     18     74      9    81%
fakeredis/stack/_cf_mixin.py                              132     27     66      9    79%
fakeredis/stack/_cms_mixin.py                              79      0     50      0   100%
fakeredis/stack/_json_mixin.py                            327     12    180     10    96%
fakeredis/stack/_tdigest_mixin.py                         173     32    118     29    79%
fakeredis/stack/_timeseries_mixin.py                      337     45    206     33    84%
fakeredis/stack/_topk_mixin.py                             77     15     48     15    76%
-----------------------------------------------------------------------------------------
TOTAL                                                    6058    470   2991    294    91%