We have no ironclad principle of never voting for “bourgeois” candidates. Socialists may advocate a vote for non-working-class, and even “bourgeois”, candidates in certain circumstances:
i) Historically when the bourgeois is completing its revolution where they are going to win bourgeois liberties and the ability for the working cass to organise.
ii) Where there is a specific positive part or parts of their programme which you want to achieve, which are of sufficient weight to demand that you support them.
iii) Where a specific group is so repressed that supporting their candidates, even bourgeois, is an act of solidarity.