An assessment of long‐range corrected density functional approximations in the calculation of the reduction potentials of Ni( S 2 C 2 H 2 ) 2 , Ni( Se 2 C 2 H 2 ) 2 , Ni( S 2 C 2 H 2 )( N 2 C 2 H 4 ), and Ni( Se 2 C 2 H 2 )( N 2 C 2 H 4 ) complexes