Add missing javadoc classpath declaration. (#3674)

Author: rlazo

appcheck/firebase-appcheck-playintegrity/firebase-appcheck-playintegrity.gradle

@@ -48,6 +48,8 @@ dependencies {
     implementation 'com.google.android.gms:play-services-tasks:18.0.1'
     implementation 'com.google.android.play:integrity:1.0.1'
 
+    javadocClasspath 'com.google.auto.value:auto-value-annotations:1.6.6'
+
     testImplementation 'junit:junit:4.13.2'
     testImplementation 'org.mockito:mockito-core:3.4.6'
     testImplementation "com.google.truth:truth:$googleTruthVersion"