Bump org.testfx:testfx-core from 4.0.17 to 4.0.18

Bumps [org.testfx:testfx-core](https://github.com/TestFX/TestFX) from 4.0.17 to 4.0.18.
- [Release notes](https://github.com/TestFX/TestFX/releases)
- [Changelog](https://github.com/TestFX/TestFX/blob/master/CHANGES.md)
- [Commits](https://github.com/TestFX/TestFX/commits)

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

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

build.gradle

@@ -351,7 +351,7 @@ dependencies {
   testImplementation("com.squareup.okhttp3:okhttp")
   testImplementation("com.squareup.okhttp3:mockwebserver")
   testImplementation("io.projectreactor:reactor-test")
-  testImplementation("org.testfx:testfx-core:4.0.17") {
+  testImplementation("org.testfx:testfx-core:4.0.18") {
     exclude module: 'guava'
   }
   testImplementation("io.projectreactor.netty:reactor-netty")