Release Exiv2 version 0.28.6 (backport #3366)

[mergify]

Update version numbers for the new release.

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This is an automatic backport of pull request #3366 done by Mergify.

[mergify]

Cherry-pick of 48c410a has failed:

On branch mergify/bp/main/pr-3366
Your branch is up to date with 'origin/main'.

You are currently cherry-picking commit 48c410a5.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   SECURITY.md
	modified:   doc/ChangeLog

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   CMakeLists.txt
	both modified:   meson.build

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally