fix(xc): restore func_type check in gradcorr stress path for mGGA

The previous commit (XC_FLAGS_NEEDS_LAPLACIAN) incorrectly replaced
'func_type == 3 || func_type == 5' with 'need_laplacian' in the stress
path of gradcorr(). This caused SCAN (func_type=3, need_laplacian=false)
to call gcxc_libxc instead of tau_xc, losing the tau-dependent v2xc
and making the GGA stress contribution zero.

Fix: use func_type check for selecting tau_xc vs gcxc_libxc (all mGGA
functionals need tau_xc), and need_laplacian only for Laplacian
computation and vlapl stress contribution.

SCAN PW stress FD: error reduced from 41.3% to 0.45%.

Author: dyzheng

source/source_hamilt/module_xc/xc_grad.cpp

@@ -475,7 +475,7 @@ void XC_Functional::gradcorr(
                     if (use_libxc && is_stress)
                     {
 #ifdef USE_LIBXC
-                        if(need_laplacian)
+                        if(func_type == 3 || func_type == 5)
                         {
                             double v3xc = 0.0;
                             double vlapl = 0.0;
@@ -540,7 +540,7 @@ void XC_Functional::gradcorr(
                     double v2xcup = 0.0;
                     double v2xcdw = 0.0;
                     double v2xcud = 0.0;
-                    if(need_laplacian)
+                    if(func_type == 3 || func_type == 5)
                     {
                         double v3xcup = 0.0;
                         double v3xcdw = 0.0;