Update dependency org.assertj:assertj-core to v3.26.3

Author: renovate[bot]

javalin-demo/gradle.properties

@@ -13,7 +13,7 @@ commonsEmail=1.6.0
 
 # Testing
 junitVersion=5.10.2
-assertjVersion=3.26.0
+assertjVersion=3.26.3
 mockitoVersion=5.12.0
 seleniumChromeVersion=4.18.1
 seleniumHttpJdkVersion=4.13.0