ci(dependabot): keep JavaFX on the line that still runs on Java 17 (#471)

JavaFX follows the JDK it was built against, and 21.x is the last line that
runs on Java 17. The CI matrix still builds and tests on 17, so the proposed
jump to 26.0.2 failed qa's compile outright: javafx-controls resolves, but
Label, TextArea, FontWeight and Font are not visible to a release-17 compile
and the JavaFX dev-preview tool stops building.

Ignoring only major bumps, so patch and minor updates inside 21.x still arrive.
The entry says when to drop it: once the matrix floor moves past 17.

Author: DemchaAV

.github/dependabot.yml

@@ -34,6 +34,14 @@ updates:
       # jackson-bom >= 2.22.1 (or 2.23.0) lands on Central with full module sync.
       - dependency-name: "com.fasterxml.jackson:jackson-bom"
         versions: ["2.22.0"]
+      # JavaFX follows the JDK it was built against: the 21.x line is the last
+      # one that runs on Java 17, and the CI matrix still builds and tests on 17.
+      # A major bump therefore fails qa's compile outright — javafx-controls 26
+      # resolves, but Label / TextArea / FontWeight are not visible to a release-17
+      # compile, so the JavaFX dev-preview tool stops building. Drop this entry
+      # when the matrix's floor moves past 17.
+      - dependency-name: "org.openjfx:*"
+        update-types: ["version-update:semver-major"]
 
   - package-ecosystem: github-actions
     directory: "/"