[INFO] cloning repository https://github.com/mb64/sudoku-solver
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/mb64/sudoku-solver" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fmb64%2Fsudoku-solver", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fmb64%2Fsudoku-solver'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 8644dd5b33c0b7ae73156dbea08020fe154967e8
[INFO] checking mb64/sudoku-solver against master#f7b43542838f0a4a6cfdb17fbeadf45002042a77 for pr-138499
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fmb64%2Fsudoku-solver" "/workspace/builds/worker-6-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-6-tc1/source'...
[INFO] [stderr] done.
[INFO] [stderr] fatal: update_ref failed for ref 'HEAD': cannot update ref 'refs/heads/master': couldn't write '/workspace/builds/worker-6-tc1/source/.git/refs/heads/master.lock'


failed to checkout https://github.com/mb64/sudoku-solver

Caused by:
    command failed: exit status: 128