[MNG-7212] Prefer use of InheritableThreadLocal to fix possible issue…

… when mojo starts a thread and tries to access some artifacts

Signed-off-by: Olivier Lamy <olamy@apache.org>

This closes #521

maven-core/src/main/java/org/apache/maven/project/MavenProject.java

@@ -147,8 +147,8 @@ public class MavenProject
 
     private Artifact artifact;
 
-    private final ThreadLocal<ArtifactsHolder> threadLocalArtifactsHolder =
-        ThreadLocal.withInitial( ArtifactsHolder::new );
+    private final InheritableThreadLocal<ArtifactsHolder> threadLocalArtifactsHolder =
+        InheritableThreadLocal.withInitial( ArtifactsHolder::new );
 
     private Model originalModel;