Update qcdnum installation

[amsimone]

I have updated the qcdnum formula to install the qcdnum-config executable and not only the libraries.

Have you:

• [ X] Run brew audit --strict --online <formula> (where <formula> is the name of the formula you're submitting) and corrected all errors?

• [X ] Built your formula locally prior to submission with brew install <formula>?

Updates to existing formula: have you

• [ X] Checked that the tests still pass?

[davidchall]

Hi @amsimone - thanks for your contribution! The GHA builds require each PR only edits a single formula, so I've recreated these changes in #333. I also kept the previous test (builds an example executable), which was more robust.