### Godot version

4.0.beta16

### System information

Windows 10 Pro x64, GLES3, RTX 3080 Ti (528.02)

### Issue description

In Compatibility/GLES3 back-end, shaders which use a uniform to get the normal roughness buffer cannot compile. For example, the shader:
```glsl
shader_type spatial;

uniform sampler2D normal_roughness_texture : hint_normal_roughness_texture;

void fragment() {
    vec4 sample = texture(normal_roughness_texture, UV);
}
```
results in an error in the output:
```
  drivers/gles3/shader_gles3.cpp:242 - SceneShaderGLES3: Fragment shader compilation failed:
  0(890) : error C1503: undefined variable "normal_roughness_buffer"
  
  drivers/gles3/shader_gles3.cpp:342 - Method/function failed.
```

If I switch over to the Mobile or Forward+ backends, there is no shader compilation error.

### Steps to reproduce

Open the attached reproduction in the 4.0.beta16 editor.

When the scene is opened, the error is produced automatically:
1. Open `scene.tscn`
2. Open Output to review error

When the scene is saved with any changes made to the shader, the same error is also produced:
1. Open `scene.tscn`
2. Open `example.gdshader` in the shader editor.
3. Make a compile-able change to the shader.
4. Save the scene
5. Open Output to review the error

### Minimal reproduction project

[NormalRoughnessTexture_GLES3_Error.zip](https://github.com/godotengine/godot/files/10534253/NormalRoughnessTexture_GLES3_Error.zip)

if (next_token.type == TK_BRACKET_OPEN) {
							_get_token(); 
							_get_token(); 
							next_token = _get_token();
						}
						_set_tkpos(prev_pos);
						ShaderNode::Varying &var = shader->varyings[identifier];
						String error;
						if (is_token_operator_assign(next_token.type)) {
							if (!_validate_varying_assign(shader->varyings[identifier], &error)) {
								_set_error(error);
								return nullptr;
							}
						} else {
							switch (var.stage) {
								case ShaderNode::Varying::STAGE_UNKNOWN: {
									if (var.type < TYPE_INT) {
										if (current_function == varying_function_names.vertex) {
											_set_error(vformat(RTR("Varying with '%s' data type may only be used in the 'fragment' function."), get_datatype_name(var.type)));
										} else {
											_set_error(vformat(RTR("Varying '%s' must be assigned in the 'fragment' function first."), identifier));
										}
										return nullptr;
									}
								} break;
								case ShaderNode::Varying::STAGE_VERTEX:
									if (current_function == varying_function_names.fragment || current_function == varying_function_names.light) {
										var.stage = ShaderNode::Varying::STAGE_VERTEX_TO_FRAGMENT_LIGHT;
									}