checkstyle.xml: masquerade a comment from 0pdd.

Work around for yegor256/0pdd#168

No functional changes.

[ci skip]

Author: php-coder

src/main/config/checkstyle.xml

@@ -262,7 +262,7 @@
                 <property name="severity" value="info"/>
             </module>
             <module name="TodoComment">
-                <property name="format" value="@todo"/>
+                <property name="format" value="&#x40;todo"/>
                 <property name="severity" value="info"/>
             </module>
         -->