Upgrade to AssertJ 3.23.1

Closes gh-838

Author: wilkinsona

spring-restdocs-platform/build.gradle

@@ -16,7 +16,7 @@ dependencies {
 		api("org.apache.pdfbox:pdfbox:2.0.7")
 		api("org.asciidoctor:asciidoctorj:2.5.4")
 		api("org.asciidoctor:asciidoctorj-pdf:2.1.4")
-		api("org.assertj:assertj-core:3.11.1")
+		api("org.assertj:assertj-core:3.23.1")
 		api("org.hamcrest:hamcrest-core:1.3")
 		api("org.hamcrest:hamcrest-library:1.3")
 		api("org.hibernate.validator:hibernate-validator:7.0.4.Final")