fix: vsce packaging failing on ci

[ottodevs]

I realised that it was tried several times to add the vsce package step to the pretest script.
Like in the commits: 2117d6a, 328a68f and 328a68f

Referring to https://stackoverflow.com/questions/70526178/error-package-vscode-extension-with-vsce-invalid-relative-path

It is easily solvable by adding the --yarn modifier, even if yarn is not installed in the system (I tested it)

So maybe this is a useful add-on to the build system, at least I hope so, feel free to discard this PR if I am wrong.