Golang os: Root.MkdirAll can return "file exists" when called concurrently on the same path [1.25 backport]

@database64128 requested issue #75114 to be considered for backport to the next 1.25 minor release.

@gopherbot please open backport issues. The fix is just an additional error check. The workaround involves calling os.Root.MkdirAll in a loop, which doesn't look very safe:

go for { if err := root.MkdirAll(path, 0755); err != nil { if errors.Is(err, os.ErrExist) { continue } return nil, err } break }

You can't put a limit on the number of retries, unless you know in advance how many path components are there.