Fix FormatStringAnnotation warning in RequiredAnnotationProcessor

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RELNOTES: Fix FormatStringAnnotation warning in RequiredAnnotationProcessor

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=260428872

core/src/main/java/com/google/errorprone/refaster/annotation/RequiredAnnotationProcessor.java

@@ -16,6 +16,8 @@
 
 package com.google.errorprone.refaster.annotation;
 
+import com.google.errorprone.annotations.FormatMethod;
+import com.google.errorprone.annotations.FormatString;
 import java.util.List;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -115,8 +117,9 @@ public Void visitArray(List<? extends AnnotationValue> vals, Void p) {
     validateElements(element.getEnclosedElements());
   }
 
+  @FormatMethod
   private void printError(
-      Element element, AnnotationMirror annotation, String message, Object... args) {
+      Element element, AnnotationMirror annotation, @FormatString String message, Object... args) {
     processingEnv
         .getMessager()
         .printMessage(Kind.ERROR, String.format(message, args), element, annotation);