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

Author: stephengold

config/checkstyle/checkstyle.xml

@@ -267,7 +267,7 @@
         <!-- Regexp checks:                           -->
         <!-- See https://checkstyle.org/checks/regexp -->
         <module name="RegexpSinglelineJava">
-            <property name="format" value="static (abstract|final|native|package|private|protected)|(native|package|private|protected) (abstract|final)"/>
+            <property name="format" value="static (abstract|final|native|private|protected|public)|(native|private|protected|public) (abstract|final)"/>
             <property name="message" value="Modifiers must appear in alphabetical order."/>
         </module>
         <module name="RegexpSinglelineJava">