Elon Musk’s social media platform X is set to be served with a formal warning for failing to combat dangerous content, in the third show of force by European Union regulators against Big Tech in recent weeks.The escalation — which could eventually pave the way for fines of 6% of X’s revenue — is likely to be announced by Internal Market Commissioner Thierry Breton before the EU’s summer recess, according to people familiar with the case who spoke on condition of anonymity....