Birmingham's cross-party leaders are facing their biggest test yet amid ongoing anger over a controversial Green Party vote on Zionism.There are renewed calls today for the Liberal Democrats to cut ties with their Green coalition partners over the issue unless they 'denounce' the vote.The city council's elected leader Roger Harmer is being targeted after members of Birmingham's Greens, including at least one Cabinet member, backed a motion declaring that 'zionism is racism' and that the party was now officially 'anti Zionist'.READ MORE: Landlord lures homeless people to Birmingham with promise of 'PS5 console or holiday'The party has itself been declared...