Fix pretty-printing of true/false keywords

Author: atextor

core/esmf-aspect-model-validator/src/main/java/org/eclipse/esmf/aspectmodel/shacl/RustLikeFormatter.java

@@ -231,6 +231,12 @@ private boolean formatNode( final RDFNode node ) {
          if ( node.asNode().equals( NodeConst.nodeRDFType ) ) {
             spacedIfPossible( "a " );
          }
+         if ( node.asNode().equals( NodeConst.nodeTrue ) ) {
+            spacedIfPossible( "true" );
+         }
+         if ( node.asNode().equals( NodeConst.nodeFalse ) ) {
+            spacedIfPossible( "false" );
+         }
          return true;
       }