Add changeset for agent bump
Add changeset for agent bump

I forgot to add the changeset in the previous commit, so I'm adding it
in this commit. See the parent of this commit for the actual agent bump.

[ci skip]

appsignal/appsignal-elixir,appsignal/appsignal-elixir,appsignal/appsignal-elixir,appsignal/appsignal-elixir