Update to 20260916; fix some license information

Ben Hutchingsrequested to merge
benh/firmware-nonfree:update-20260916 into debian/latest
  • d/changelog: Add new upstream version, summarising the many amdgpu reverts
  • d/copyright: Update for new upstream version

Then fix some problems in d/copyright that I noticed while updating it for the new version:

  • d/copyright: Correct license text for Dell XPS13 9345 GPU firmware
  • d/copyright: Change some short names to identify variants of the MIT license

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