Fix alpha scissor support

(cherry picked from commit 2fb998bfbc6daddc2d5b311d489fb01c782c4c3b)

drivers/gles2/rasterizer_storage_gles2.cpp

@@ -1952,7 +1952,7 @@ void RasterizerStorageGLES2::_update_material(Material *p_material) {
 
 		if (p_material->shader && p_material->shader->mode == VS::SHADER_SPATIAL) {
 			if (p_material->shader->spatial.blend_mode == Shader::Spatial::BLEND_MODE_MIX &&
-					(!p_material->shader->spatial.uses_alpha || p_material->shader->spatial.depth_draw_mode == Shader::Spatial::DEPTH_DRAW_ALPHA_PREPASS)) {
+					(!(p_material->shader->spatial.uses_alpha && !p_material->shader->spatial.uses_alpha_scissor) || p_material->shader->spatial.depth_draw_mode == Shader::Spatial::DEPTH_DRAW_ALPHA_PREPASS)) {
 				can_cast_shadow = true;
 			}
 

drivers/gles3/rasterizer_storage_gles3.cpp

@@ -3153,7 +3153,7 @@ void RasterizerStorageGLES3::_update_material(Material *material) {
 
 		if (material->shader && material->shader->mode == VS::SHADER_SPATIAL) {
 			if (material->shader->spatial.blend_mode == Shader::Spatial::BLEND_MODE_MIX &&
-					(!material->shader->spatial.uses_alpha || material->shader->spatial.depth_draw_mode == Shader::Spatial::DEPTH_DRAW_ALPHA_PREPASS)) {
+					(!(material->shader->spatial.uses_alpha && !material->shader->spatial.uses_alpha_scissor) || material->shader->spatial.depth_draw_mode == Shader::Spatial::DEPTH_DRAW_ALPHA_PREPASS)) {
 				can_cast_shadow = true;
 			}