Gradle: Bump io.undertow:undertow-core from 2.3.16.Final to 2.3.18.Final

Bumps [io.undertow:undertow-core](https://github.com/undertow-io/undertow) from 2.3.16.Final to 2.3.18.Final.
- [Release notes](https://github.com/undertow-io/undertow/releases)
- [Commits](undertow-io/undertow@2.3.16.Final...2.3.18.Final)

---
updated-dependencies:
- dependency-name: io.undertow:undertow-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build.gradle.kts

@@ -279,7 +279,7 @@ subprojects {
     implementation("org.springframework.boot:spring-boot-starter-undertow") {
       constraints {
         implementation("org.jboss.xnio:xnio-api:3.8.16.Final")
-        implementation("io.undertow:undertow-core:2.3.16.Final")
+        implementation("io.undertow:undertow-core:2.3.18.Final")
       }
     }
     implementation("com.fasterxml.jackson.module:jackson-module-kotlin:2.18.3")