Fix global shader texture uniform

[beicause]

Fixes #107470

global_shader_parameter_add can add a Texture2D object as a shader parameter, and it is implicitly converted to RID:

godot/core/variant/variant.cpp

Line 2017 in 591e70f

const Variant ret = _get_obj().obj->callp(CoreStringName(get_rid), nullptr, 0, ce);

Additionally we can save the RID before textures.push_back() to avoid converting it twice..

[akien-mga]

Makes sense to me.

[akien-mga]

Thanks!

[dsnopek]

Thanks for catching this! (And sorry for introducing the regression :-/)

I just tested these changes with the original MRP from issue #101938, and that issue is still fixed with these new changes :-)