Modify test-expand.sh so that test binary is generated as a tmp file

[TonalidadeHidrica]

Currently, .github/workflows/test-expand.sh runs rustc that creates a binary named test in the current working directory. This is a bit troublesome when testing locally because it creates an untracked binary file in the repository. Woo, dangerous. Let's set a option so that rustc generates a binary in the /tmp directory instead!