fix(xtask): read ci.yml's wrapped commands under either line ending

The first run of `tests (windows)` failed in exactly one place, and it was this runner's own drift check: `workflow_commands` joined a wrapped command by replacing backslash-LF, and a Windows checkout hands the test `ci.yml` with CRLF, so the multi-line `cargo doc` step kept its backslashes and no longer matched the runner's plan. It now walks `lines()`, which drops either ending, and strips the trailing backslash; a small test pins both endings so the next regression shows up on any host. Every other Windows test — including the thirty-three that had never executed before — passed on that first run.