feat(CodeExecutable): Add `DependenciesFailed` variant to `executeRequired`
feat(CodeExecutable): Add `DependenciesFailed` variant to `executeRequired`

stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila