Change: make GOG more like MSStore/Steam for OpenGFX

OpenGFX for the other platforms is untar'd. There is no real need
to do this, but there is also no hurt in not doing it. And doing
the same for all three has more benefits than having one being
different.

.github/workflows/upload-gog.yml

@@ -62,9 +62,10 @@ jobs:
 
         echo "::group::Unpack OpenGFX"
         unzip opengfx-all.zip
+        tar xf opengfx-*.tar
         echo "::endgroup::"
 
-        rm -f opengfx-all.zip
+        rm -f opengfx-all.zip opengfx-*.tar
 
     - name: Install OpenMSX
       shell: bash