Merge branch '175-error-in-dia_hth_dep-when-calculating-26-28-deg-isotherm-depth' into 'branch_4.2'

Resolve "Error in `dia_hth_dep` when calculating 26/28 deg isotherm depth" ('branch_4.2')

See merge request nemo/nemo!288

src/OCE/DIA/diahth.F90

@@ -326,8 +326,8 @@ CONTAINS
          iid = iktem(ji,jj)
          IF( iid /= 1 ) THEN 
              zztmp =     gdept(ji,jj,iid  ,Kmm)   &                     ! linear interpolation
-               &  + (    gdept(ji,jj,iid+1,Kmm) - gdept(ji,jj,iid,Kmm)                       )   &
-               &  * ( 20.*tmask(ji,jj,iid+1) - ts(ji,jj,iid,jp_tem,Kmm)                       )   &
+               &  + (    gdept(ji,jj,iid+1,Kmm) - gdept(ji,jj,iid,Kmm)                            )   &
+               &  * ( ptem * tmask(ji,jj,iid+1)  - ts(ji,jj,iid,jp_tem,Kmm)                       )   &
                &  / ( ts(ji,jj,iid+1,jp_tem,Kmm) - ts(ji,jj,iid,jp_tem,Kmm) + (1.-tmask(ji,jj,1)) )
             pdept(ji,jj) = MIN( zztmp , zzdep) * tmask(ji,jj,1)       ! bound by the ocean depth
          ELSE