fix ConcurrentModificationException at v2-migration (#5665)

This fixes a ConcurrentModificationException that occured running the
OpenRewrite recipe by replacing a HashMap with a ConcurrentHashMap

Co-authored-by: Debora N. Ito <[email protected]>

Author: sk-br

.changes/next-release/bugfix-v2migrationOpenRewriterecipe-86404ba.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "v2-migration OpenRewrite recipe",
+    "contributor": "sk-br",
+    "description": "This fixes a ConcurrentModificationException - just by replacing a HashMap with ConcurrentHashMap"
+}

v2-migration/src/main/java/software/amazon/awssdk/v2migration/ChangeSdkType.java

@@ -22,14 +22,14 @@
 import static software.amazon.awssdk.v2migration.internal.utils.SdkTypeUtils.isV1ModelClass;
 
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 import java.util.Stack;
+import java.util.concurrent.ConcurrentHashMap;
 import org.openrewrite.ExecutionContext;
 import org.openrewrite.Recipe;
 import org.openrewrite.TreeVisitor;
@@ -88,7 +88,7 @@ private static class ChangeTypeVisitor extends JavaVisitor<ExecutionContext> {
         private final Set<String> topLevelClassnames = new HashSet<>();
         private final List<String> wildcardImports = new ArrayList<>();
 
-        private Map<String, Pair<JavaType.Class, JavaType>> oldTypeToNewType = new HashMap<>();
+        private Map<String, Pair<JavaType.Class, JavaType>> oldTypeToNewType = new ConcurrentHashMap<>();
 
         @Override
         public J visitClassDeclaration(J.ClassDeclaration classDecl, ExecutionContext ctx) {