test: adding os-matrix for unit tests

[axel7083]

Description

When trying to investigate #38 I find out that the problem was only occurring on Windows.

The problem is occurring in the code below, the is_absolute is platform specific.

compose_spec_rs/src/service/volumes.rs

Lines 310 to 314 in 1c6924b

	if path.as_ref().is_absolute() {
	Ok(Self(path.into()))
	} else {
	Err(AbsolutePathError)
	}

Quoting the rust documentation

Returns true if the Path is absolute, i.e., if it is independent of the current directory.

• On Unix, a path is absolute if it starts with the root, so is_absolute and has_root are equivalent.
• On Windows, a path is absolute if it has a prefix and starts with the root: c:\windows is absolute, while c:temp and \temp are not.

Source https://doc.rust-lang.org/std/path/struct.Path.html

The ContainerPath is always POSIX, so the is_absolute cannot be used on it, since on windows it would fails

Context

This PR does not fix the problem, as I am not familiar with the code, and with the numerous usage of the AbsolutePath struct I don't want to risk to break everything!

This PR is adding an os-matrix for testing. (Today it fails, but if #38 is fixed, a simple rebase should be enough)