Backport #12189: user manual: update copyright year to 2026

[mergify]

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Template B: This PR does not modify behaviour or interface

E.g. the PR only touches documentation or tests, does refactorings, etc.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

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This is an automatic backport of pull request #12189 done by [Mergify](https://mergify.com).

[Mikolaj]

Perfect in all respect.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-07-31 22:22 UTC · Rule: squash-merge · triggered by rule Put backports in the squash+merge queue
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-07-31 22:34 UTC · at 55aa180fa5c1fc1a909798891a05f32e3f35cfbe · squash

This pull request spent 11 minutes 11 seconds in the queue, including 3 seconds running CI.

Required conditions to merge

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  • Backport #12189: user manual: update copyright year to 2026 #12195
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  • Backport #12189: user manual: update copyright year to 2026 #12195
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