Apply transactionIsolationLock in EclipseLinkConnectionHandle as well

Closes gh-36165

(cherry picked from commit 2b96a61063)

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java

@@ -168,7 +168,7 @@ public class EclipseLinkJpaDialect extends DefaultJpaDialect {
 	 * This is useful to defer the early transaction begin that obtaining a
 	 * JDBC Connection implies within an EclipseLink EntityManager.
 	 */
-	private static class EclipseLinkConnectionHandle implements ConnectionHandle {
+	private class EclipseLinkConnectionHandle implements ConnectionHandle {
 
 		private final EntityManager entityManager;
 
@@ -182,7 +182,13 @@ public class EclipseLinkJpaDialect extends DefaultJpaDialect {
 		@Override
 		public Connection getConnection() {
 			if (this.connection == null) {
-				this.connection = this.entityManager.unwrap(Connection.class);
+				transactionIsolationLock.lock();
+				try {
+					this.connection = this.entityManager.unwrap(Connection.class);
+				}
+				finally {
+					transactionIsolationLock.unlock();
+				}
 			}
 			return this.connection;
 		}