chore: update concerto dependencies

[jamieshorten]

Updates the Concerto dependencies.

Changes

updates:

@accordproject/concerto-cto": "3.19.6",
"@accordproject/concerto-core": "3.19.6",
"@accordproject/concerto-util": "3.19.6",
"@accordproject/concerto-vocabulary": "3.19.6",

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

[coveralls]

coverage: 98.771%. remained the same
when pulling 96850d8 on jamieshorten:main
into 3347cdb on accordproject:main.