Set Asciidoctor attribute-missing to warn

Closes gh-26590

Author: philwebb

spring-boot-project/spring-boot-actuator-autoconfigure/src/docs/asciidoc/index.adoc

@@ -7,6 +7,7 @@ Andy Wilkinson
 :icons: font
 :hide-uri-scheme:
 :docinfo: shared,private
+:attribute-missing: warn
 
 This API documentation describes Spring Boot Actuators web endpoints.
 

spring-boot-project/spring-boot-docs/src/docs/asciidoc/attributes.adoc

@@ -9,6 +9,7 @@
 :sectnums:
 :hide-uri-scheme:
 :docinfo: shared,private
+:attribute-missing: warn
 :chomp: default headers packages
 :spring-boot-artifactory-repo: snapshot
 :github-tag: main

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/index.adoc

@@ -8,6 +8,7 @@ Andy Wilkinson, Scott Frederick
 :icons: font
 :hide-uri-scheme:
 :docinfo: shared,private
+:attribute-missing: warn
 
 :dependency-management-plugin: https://github.com/spring-gradle-plugins/dependency-management-plugin
 :dependency-management-plugin-documentation: https://docs.spring.io/dependency-management-plugin/docs/current/reference/html/

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/docs/asciidoc/index.adoc

@@ -8,6 +8,7 @@ Stephane Nicoll, Andy Wilkinson, Scott Frederick
 :icons: font
 :hide-uri-scheme:
 :docinfo: shared,private
+:attribute-missing: warn
 
 :buildpacks-reference: https://buildpacks.io/docs
 :spring-boot-docs: https://docs.spring.io/spring-boot/docs/{gradle-project-version}