1.3.11 - Multiple small fixes

Enhancements

• No op Dsl::WorkatoPackage#parse_json unless input is a String. Workato docs
• Raise custom error when Workato::Extension::String#+ argument is nil.
• Operation#schema_fields to always return an array

Misc

• Keep BlockInvocationRefinements::BasicObject#instance_exec ruby 2.7 behaviour in ruby 3.0+
• Code polishing & refactoring