Bump org.assertj:assertj-core in /tools/gradle-plugin

Bumps [org.assertj:assertj-core](https://github.com/assertj/assertj) from 3.26.0 to 3.26.3.
- [Release notes](https://github.com/assertj/assertj/releases)
- [Commits](assertj/assertj@assertj-build-3.26.0...assertj-build-3.26.3)

---
updated-dependencies:
- dependency-name: org.assertj:assertj-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

tools/gradle-plugin/build.gradle

@@ -37,7 +37,7 @@ dependencies {
 
     testImplementation("org.junit.jupiter:junit-jupiter:${versionJunit5}")
     testImplementation(gradleTestKit())
-    testImplementation("org.assertj:assertj-core:3.26.0")
+    testImplementation("org.assertj:assertj-core:3.26.3")
     testImplementation("com.fasterxml.jackson.core:jackson-databind:${versionJackson}")
 }