WebGPURenderer: getTextureLevel of background should multiply maxMipLevel

[susiwen8]

Before	After
Screen.Recording.2024-02-26.at.14.11.18.mov	Screen.Recording.2024-02-26.at.14.07.22.mov

const equirectTexture = new THREE.TextureLoader().load( 'textures/2294472375_24a3b8ef46_o.jpg' );
equirectTexture.flipY = false;
equirectTexture.mapping = THREE.EquirectangularReflectionMapping;
equirectTexture.colorSpace = THREE.SRGBColorSpace;

scene = new THREE.Scene();
scene.background = equirectTexture;


scene.backgroundBlurriness = .5;