Fix #137052: GPU: Crash on startup caused by legacy pyGPU API

The removed legacy API was still in used by the pyGPU API.
Add a deprecation warning instead.

This partially reverts commit 3179cb0069.

source/blender/python/gpu/gpu_py_shader.cc

@@ -109,6 +109,11 @@ static PyObject *pygpu_shader__tp_new(PyTypeObject * /*type*/, PyObject *args, P
 {
   BPYGPU_IS_INIT_OR_ERROR_OBJ;
 
+  PyErr_WarnEx(PyExc_DeprecationWarning,
+               "Direct shader creation is deprecated. "
+               "Use gpu.shader.create_from_info(shader_info) instead.",
+               1);
+
   struct {
     const char *vertexcode;
     const char *fragcode;