`fbrnch parallel` with chain builds does not parallelize the branches

[LecrisUT]

I was running

$ fbrnch parallel --sidetag -m f42 f41 epel9 rust-sqlx-core : rust-sqlx-macros-core : rust-sqlx-macros rust-sqlx-sqlite rust-sqlx-postgres rust-sqlx-mysql : rust-sqlx

But the f41 and epel9 are not executed in parallel with f42

Edit: ~~oh wait, the other builds are also not parallelized?~~ Nvm, I didn't pay attention to what it was doing in parallel