Do we correctly populate `to_branch` for MR refs?

[MisterDA]

Saw that the target branch defaults to master in the code. Is the default overwritten? It could be main instead or any other name. I don't think we're going to have the right value here, but on the other hand I'm not sure that we actually use it.

tezos-ci/src/tezos_ci.ml

Line 37 in 96ee5b5

{ from_branch = string_of_int number; to_branch = "master" }

[tmcgilchrist]

https://gitlab.com/tezos/tezos/ uses master for it's default branch name, so I don't think this is an issue here. For something like ocaml-ci it could be.

Having said that the default branch is queryable via REST API and is available at

tezos-ci/src/tezos_ci.ml

Line 47 in 96ee5b5

let default_ref = Gitlab.Api.default_ref refs in

so why not just use that?