t8*: adjust the references to the default branch name "main"

[git] / t / chainlint / multi-line-nested-command-substitution.test

(
        foo &&
        x=$(
                echo bar |
                cat
        ) &&
        echo ok
) |
sort &&
(
        bar &&
        x=$(echo bar |
                cat
        ) &&
        y=$(echo baz |
                fip) &&
        echo fail
)