[MNG-8341] Fix possible deadlock in ModelBuilder (#1843)

The deadlock can happen when the root pom inherit from a parent which is a subproject, the subproject inheriting from an external parent.

maven-api-impl/src/main/java/org/apache/maven/internal/impl/model/DefaultModelBuilder.java

@@ -921,7 +921,7 @@ private Model readParentLocally(Model childModel) throws ModelBuilderException {
             if (candidateSource == null) {
                 candidateSource = resolveReactorModel(parent.getGroupId(), parent.getArtifactId(), parent.getVersion());
             }
-            if (candidateSource == null) {
+            if (candidateSource == null && parentPath == null) {
                 candidateSource = request.getSource().resolve(modelProcessor::locateExistingPom, "..");
             }