Regression from #71248:

I believe this pull may have caused errors on WebGL since it moves the `GLES_OVER_GL` guard. WebGL does not support texture swizzling per: https://registry.khronos.org/webgl/specs/latest/2.0/#5.19
so this is causing the following trace in Chrome:
```
WebGL: INVALID_ENUM: texParameter: invalid parameter name
```
and it quickly fills up the 256 log limit for the same message in WebGL.

This doesn't appear to be breaking anything asides from causing the numerous log messages.

_Originally posted by @jnlopar in https://github.com/godotengine/godot/issues/71248#issuecomment-1384768973_

CC @rsjtdrjgfuzkfg @clayjohn
RenderTarget *rt = render_target_owner.get_or_null(p_render_target);
	ERR_FAIL_COND(!rt);
	ERR_FAIL_COND(rt->direct_to_screen);
	if (rt->backbuffer_fbo == 0) {
		_create_render_target_backbuffer(rt);
	}
	Rect2i region;
	if (p_region == Rect2i()) {
		
		glBindFramebuffer(GL_FRAMEBUFFER, rt->backbuffer_fbo);
		glClearColor(p_color.r, p_color.g, p_color.b, p_color.a);
		glClear(GL_COLOR_BUFFER_BIT);
	} else {
		region = Rect2i(Size2i(), rt->size).intersection(p_region);
		if (region.size == Size2i()) {
			return; 
		}
		glBindFramebuffer(GL_FRAMEBUFFER, rt->backbuffer_fbo);
		GLES3::CopyEffects::get_singleton()->set_color(p_color, region);
	}
}
void TextureStorage::render_target_gen_back_buffer_mipmaps(RID p_render_target, const Rect2i &p_region) {