The equations of two sides of a variable triangle are \( x=0 \) and \( y=3 \), and its third side is a tangent to the parabola \( y^{2}=6x \). The locus of its circumcentre is:
\( 4y^{2}-18y-3x+18=0 \)
\( 4y^{2}-18y+3x+18=0 \)
\( 4y^{2}+18y+3x+18=0 \)
\( 4y^{2}-18y-3x-18=0 \)