Do unopened bottles of Gin and Campari turn bad in extreme heat?
It won't turn bad, in fact it may make it last longer. You may have madeira-ized it (see below)

Madeira wine is known for it's extended "shelf life" after opening because of it's unique process of being heated to as high as 60 degrees C (140 F).

You may find that in the Campari some of the sugar may have crystalised. This may slightly affect the flavour, but it most certainly won't make it turn bad.