Grant write permissions for contents in release workflow

[ulysses4ever]

avoid

GitHub release failed with status: 403
Resource not accessible by integration
Skip retry — your GitHub token/PAT does not have the required permission to create a release

in the release workflow

e.g. https://github.com/haskell/cabal/actions/runs/30353923781

---

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).

[ffaf1]

Thanks!