TextStringBuilderTest#testAppendToStringBuffer appends to StringBuffer now (#724)

Co-authored-by: TheRealHaui <[email protected]>

Author: TheRealHaui

src/test/java/org/apache/commons/text/TextStringBuilderTest.java

@@ -246,7 +246,7 @@ void testAppendToCharBuffer() throws Exception {
     @Test
     void testAppendToStringBuffer() throws Exception {
         final TextStringBuilder sb = new TextStringBuilder("1234567890");
-        final StringBuilder buffer = new StringBuilder("Test ");
+        final StringBuffer buffer = new StringBuffer("Test ");
 
         sb.appendTo(buffer);