Running `pulumi` operations in parallel could occasionally result in truncating the `~/.pulumi/credentials.json` file and reading that truncated file from another process before the content could be written.
Instead, use `os.Rename` to atomically replace the file contents.
Concurrent `pulumi` operations could still compete for who gets to write the file first, and could lead to surprising results in some extreme cases. But we should not see the corrupted file contents any longer.
Fixes#3877.
9e955241fc