Fix mistaken use of dollar sign in cddl files

[teodanciu]

Description

At the moment , cddl generate that we use for cddl roundtrips does NOT generate values for these types that we prefixed with $.
The types for which values ARE generated correctly that are prefixed with $ (eg: $hash28, $vkey), are also defined in the same way, prefixed by dollar.

It's not very clear from the spec that this should be the case, but running cddl generate makes it clear that it's simply ignoring $required_signers, $treasury_withdrawals_action and $new_committee when defined in the way they are currently in the cddl.

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

[teodanciu]

If you want to test this yourself, do this:

1. Create a file a.cddl with this content:

required_signers = nonempty_set<$addr_keyhash>
addr_keyhash          = $hash28
$hash28 /= bytes .size 28
nonempty_set<a> = [+ a]

2. run: nix-shell -p cddl
3. run: cddl a.cddl generate 1
4. observe the error
5. change first line in a.cddl to required_signers = nonempty_set<addr_keyhash>
6. run: cddl a.cddl generate 1

The reason we don't get an error in tests is because it's optional this in transaction_body:
, ? 14 : required_signers

[lehins]

If only CDDL had a type checker 😉

Very nice find! Thank you.

[JaredCorduan]

wow, great catch!