checkstyle.xml: add "public" and remove "package" from modifier lists

Author: stephengold

config/checkstyle/checkstyle.xml

@@ -283,7 +283,7 @@
         <!-- Regexp checks:                           -->
         <!-- See https://checkstyle.org/checks/regexp -->
         <module name="RegexpSinglelineJava">
-            <property name="format" value="static (abstract|final|package|private|protected)|(package|private|protected) (abstract|final)"/>
+            <property name="format" value="static (abstract|final|private|protected|public)|(private|protected|public) (abstract|final)"/>
             <property name="message" value="Modifiers must appear in alphabetical order."/>
         </module>
         <module name="RegexpSinglelineJava">