fix json syntax

[flisk]

This fixes a JSON syntax error in the Pleroma Emoji pack manifest that prevents imports via pleroma_ctl.

With the error present, this happens:

$ pleroma_ctl emoji get-packs -m https://raw.githubusercontent.com/SymTrkl/emoji/refs/heads/main/pleroma-manifest/manifest.json neobot

12:44:21.531 [debug] Outbound: get https://raw.githubusercontent.com/SymTrkl/emoji/refs/heads/main/pleroma-manifest/manifest.json
** (Jason.DecodeError) unexpected byte at position 7904: 0x22 ("\"")
    lib/jason.ex:92: Jason.decode!/2
    lib/mix/tasks/pleroma/emoji.ex:45: Mix.Tasks.Pleroma.Emoji.run/1
    nofile:1: (file)
    (stdlib 5.0.2) erl_eval.erl:750: :erl_eval.do_apply/7
    (elixir 1.15.4) lib/code.ex:543: Code.validated_eval_string/3