Fix BasisUniversal ETC RA_AS_RG transcoding

(cherry picked from commit 51ad937532fb2c00f89326ac1e102a56829df2ae)

modules/basis_universal/register_types.cpp

@@ -221,7 +221,7 @@ static Ref<Image> basis_universal_unpacker_ptr(const uint8_t *p_data, int p_size
 				imgfmt = Image::FORMAT_DXT5_RA_AS_RG;
 			} else if (RS::get_singleton()->has_os_feature("etc2")) {
 				format = basist::transcoder_texture_format::cTFETC2; // get this from renderer
-				imgfmt = Image::FORMAT_ETC2_RGBA8;
+				imgfmt = Image::FORMAT_ETC2_RA_AS_RG;
 			} else {
 				//opengl most likely, bad for normal maps, nothing to do about this.
 				format = basist::transcoder_texture_format::cTFRGBA32;