### 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)

identifier = StringName();
	TkPos pos = { 0, 0 };
	Token tk = _get_token();
	if (tk.type == TK_IDENTIFIER) {
		identifier = tk.text;
		pos = _get_tkpos();
		tk = _get_token();
	}
	if (tk.type == TK_CURSOR) {
		completion_type = p_type;
		completion_line = tk_line;
		completion_block = p_block;
		pos = _get_tkpos();
		tk = _get_token();
		if (tk.type == TK_IDENTIFIER) {
			identifier = identifier.operator String() + tk.text.operator String();
		} else {
			_set_tkpos(pos);
		}
		return true;
	} else if (identifier != StringName()) {
		_set_tkpos(pos);
	}
	return false;
}
bool ShaderLanguage::_is_operator_assign(Operator p_op) const {