Fix AlonzoPlutusPurpose CBOR instances

[aniketd]

Description

Closes #4110

Checklist

• [x] Commits in meaningful sequence and with useful messages.
• [x] Tests added or updated when needed.
• [ ] CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• [ ] Versions updated in .cabal and CHANGELOG.md files when necessary, according to the versioning process.
• [ ] Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• [x] Code formatted (use scripts/fourmolize.sh).
• [x] Cabal files formatted (use scripts/cabal-format.sh).
• [x] CDDL files are up to date (use scripts/gen-cddl.sh)
• [x] hie.yaml updated (use scripts/gen-hie.sh).
• [ ] Self-reviewed the diff.