chore(deps): bump org.openjfx:javafx-fxml from 20.0.2 to 21

Bumps org.openjfx:javafx-fxml from 20.0.2 to 21.

---
updated-dependencies:
- dependency-name: org.openjfx:javafx-fxml
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

build.gradle

@@ -80,7 +80,7 @@ dependencies {
   testImplementation "org.testfx:testfx-junit5:4.0.17"
 
   // JavaFX
-  implementation "org.openjfx:javafx-fxml:20.0.2"
+  implementation "org.openjfx:javafx-fxml:21"
   implementation "org.openjfx:javafx-base:20.0.2"
   implementation "org.openjfx:javafx-controls:20.0.2"
   implementation "org.openjfx:javafx-graphics:20.0.2"