CI: Remove Linux Next (Qt 6.10) job

It has been failing for 4 consecutive weeks.

Master passes with Qt 6.10 so hopefully no one will be using this
version with 6.10...

.gitlab-ci.yml

@@ -10,7 +10,7 @@ include:
       - /gitlab-templates/yaml-lint.yml
       - /gitlab-templates/android-qt6.yml
       - /gitlab-templates/linux-qt6.yml
-      - /gitlab-templates/linux-qt6-next.yml
+      # - /gitlab-templates/linux-qt6-next.yml
       - /gitlab-templates/windows-qt6.yml
       # - /gitlab-templates/freebsd-qt6.yml
       - /gitlab-templates/flatpak.yml