[bug] cannot sync workspace when packages declare `busted` test runner

When a workspace contains two packages that each declare the `busted` test backend, syncing the workspace fails with `Error: cannot install duplicate entrypoints: busted`. MRE: ```shell mkdir -p test_ws/{proj1,proj2} cd test_ws # workspace lux.toml cat <<EOF > lux.toml [workspace] members = ["proj1", "proj2"] EOF # project 1 cat <<EOF > proj1/lux.toml package = "proj1" lua = ">=5.1" [test] type = "busted" EOF # project 2 cat <<EOF > proj2/lux.toml package = "proj2" lua = ">=5.1" [test] type = "busted" EOF lx --lua-version 5.1 sync ```