fix ghcup-0.0.4.yaml

Windows is an unknown platform in < 0.1.15

Previously:

[ Error ] JSON decoding failed with: AesonException "Error in $.ghcupDownloads.GHCup['0.1.15.1'].viArch['A_64'].Windows: Failure in Platform (FromJSONKey)"

merged

Shouldn't release after midnight. ..and CI wouldn't have catched it, since it only tests the latest yaml...