Spectroscopic study of the $\bm{4f^{7}6s^{2}\;{}{ }^8S^\circ_{7/2} - 4f^{7}({}^{8}S^\circ)6s6p ({}^{1}P^\circ)\: {}^8P_{9/2}}$ transition in neutral Europium-151 and Europium-153: absolute energy and hyperfine structure