C-380/23, Monmorieux: Judgment of the Court (Sixth Chamber) of 13 June 2024 (request for a preliminary ruling from the Tribunal de première instance du Luxembourg – Belgium) – UN v État belge (Reference for a preliminary ruling – Article 19 TEU – Article 45 TFEU – Article 47 of the Charter of Fundamental Rights of the European Union – Income tax – Convention for the avoidance of double taxation – Mutual agreement procedure provided for under such a convention – Member State, at the end of that procedure, making the right to restitution of tax already paid in another Member State conditional upon the withdrawal by the taxpayer of his or her actions brought before the courts of that first Member State – Inadmissibility of the request for a preliminary ruling)