IPreviewUrlResponse in client.d.ts has invalid types

The current (18.1.0) exported types for the interface are as follows:

export interface IPreviewUrlResponse {
    [key: string]: string | number;
    "og:title": string;
    "og:type": string;
    "og:url": string;
    "og:image"?: string;
    "og:image:type"?: string;
    "og:image:height"?: number;
    "og:image:width"?: number;
    "og:description"?: string;
    "matrix:image:size"?: number;
}

However, the undefined values do not satisfy the index constraint which leads to Typescript complaining that:

node_modules/matrix-js-sdk/lib/client.d.ts:305:5 - error TS2411: Property '"og:image:type"' of type 'string | undefined' is not assignable to 'string' index type 'string | number'.

Start at the IPreviewUrlResponse declaration around line 305 of lib/client.d.ts and reproduce the reported TypeScript compiler error with the current declarations. Check the optional properties against the index signature and confirm that the declaration compiles without TS2411 in a consuming TypeScript project.