docs: Update SpannerSample.java to align with best practices

samples/snippets/src/main/java/com/example/spanner/SpannerSample.java

@@ -679,24 +679,25 @@ static void readOnlyTransaction(DatabaseClient dbClient) {
     // ReadOnlyTransaction must be closed by calling close() on it to release resources held by it.
     // We use a try-with-resource block to automatically do so.
     try (ReadOnlyTransaction transaction = dbClient.readOnlyTransaction()) {
-      ResultSet queryResultSet =
+      try (ResultSet queryResultSet =
           transaction.executeQuery(
-              Statement.of("SELECT SingerId, AlbumId, AlbumTitle FROM Albums"));
-      while (queryResultSet.next()) {
-        System.out.printf(
-            "%d %d %s\n",
-            queryResultSet.getLong(0), queryResultSet.getLong(1), queryResultSet.getString(2));
-      }
+              Statement.of("SELECT SingerId, AlbumId, AlbumTitle FROM Albums"))) {
+        while (queryResultSet.next()) {
+          System.out.printf(
+              "%d %d %s\n",
+              queryResultSet.getLong(0), queryResultSet.getLong(1), queryResultSet.getString(2));
+        }
+      } // queryResultSet.close() is automatically called here
       try (ResultSet readResultSet =
           transaction.read(
-              "Albums", KeySet.all(), Arrays.asList("SingerId", "AlbumId", "AlbumTitle"))) {
+            "Albums", KeySet.all(), Arrays.asList("SingerId", "AlbumId", "AlbumTitle"))) {
         while (readResultSet.next()) {
           System.out.printf(
               "%d %d %s\n",
               readResultSet.getLong(0), readResultSet.getLong(1), readResultSet.getString(2));
         }
-      }
-    }
+      } // readResultSet.close() is automatically called here
+    } // transaction.close() is automatically called here
   }
   // [END spanner_read_only_transaction]