BAEL-4665: add text blocks to multiline strings test (#10777)

* BAEL-4665: add text blocks to multiline strings test

* BAEL-4665: move core-java-strings to jdk9 profile

core-java-modules/core-java-strings/src/test/java/com/baeldung/multiline/MultiLineStringUnitTest.java

@@ -16,6 +16,7 @@ public class MultiLineStringUnitTest {
         assertEquals(ms.stringJoin(), ms.stringBuilder());
         assertEquals(ms.stringBuilder(), ms.guavaJoiner());
         assertEquals(ms.guavaJoiner(), ms.loadFromFile());
+        assertEquals(ms.loadFromFile(), ms.textBlocks());
     }
     
 }