[rebar3_efmt] Explicitly specify {ssl, [{verify, verify_none}]} option

[sile]

Erlang OTP 26-rc2 has changed the default value of verify option (see the release note), and rebar3_efmt plugin installation gets failed due to the following error if OTP 26-rc2 is used:

===> No `efmt` binary found. Trying installing a pre-built binary.
===> Pre-built binary URL: "https://github.com/sile/efmt/releases/download/0.14.0/efmt-0.14.0.aarch64-apple-darwin"
===> Failed to install a pre-built binary ({http_get_failed,
                                                       {failed_connect,
                                                        [{to_address,
                                                          {"github.com",443}},
                                                         {inet,
                                                          [inet],
                                                          {options,
                                                           {verify,
                                                            {missing_dep_cacertfile_or_cacerts}}}}]}}).

This PR fixes this issue by explicitly specifying {ssl, [{verify, verify_none}]} option to httpc:request().