Ensure DRepRegistration certificate requires a witness

[TimSheard]

Change 'getScriptWitnessConwayTxCert' so that DRepRegistration certificate requires a witness

Fix #3890

Description

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[lehins]

We also need to change the getVKeyWitnessConwayTxCert that enforces the Key Witnesses

https://github.com/input-output-hk/cardano-ledger/blob/afedb7d519761ccdd9c013444aa4b3e0bf0e68ef/eras/conway/impl/src/Cardano/Ledger/Conway/TxCert.hs#L642

[lehins]

👍