Add Dune 2.8.0 release to the website

This seems to work now (tested locally) apart from one thing:

• Somehow the sorting decides that DUNE 2.8.0 should be last and not first as it should be. I have no idea why and am giving up...

added 1 commit

• 233da134 - Add a new entry for the Dune 2.8.0 release.

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added 1 commit

• d4a120f8 - Fix case of title for correct ordering.

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Ordering fixed by DUNE -> Dune. Never would have thought of this one.

mentioned in commit 1a4fd197

merged