Fix OEP full - spin polarized case

Description

The OEP full was not taking the right occupations for the spin-polarized case.

News snippet

The OEP full was not taking the right occupations for the spin-polarized case.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

testsuite/finite_systems_3d/07-spin_orbit_coupling.test

@@ -74,7 +74,7 @@ if(available scalapack); then
     match ;  Force          ; GREPFIELD(static/info, 'Forces on the ions', 3, 2) ; -9.79333089E-01
   endif
 else
-  match ; Error match ; GREPCOUNT(err, 'can only be used in parallel') ; 1
+  match ; Error match ; GREPCOUNT(err, 'scalapack subspace diagonalization') ; 1
 endif
   
 Precision : default