Remove references to internal js-sdk type CryptoBackend (#12321)

* Remove references to internal js-sdk type `CryptoBackend`

* Use `Paramteters` to avoid `ts-ignore`

test/components/views/rooms/EventTile-test.tsx

@@ -29,7 +29,6 @@ import {
     TweakName,
 } from "matrix-js-sdk/src/matrix";
 import { EventEncryptionInfo, EventShieldColour, EventShieldReason } from "matrix-js-sdk/src/crypto-api";
-import { CryptoBackend } from "matrix-js-sdk/src/common-crypto/CryptoBackend";
 import { TooltipProvider } from "@vector-im/compound-web";
 
 import EventTile, { EventTileProps } from "../../../../src/components/views/rooms/EventTile";
@@ -320,8 +319,7 @@ describe("EventTile", () => {
                     decryptEvent: async (_ev): Promise<IEventDecryptionResult> => {
                         throw new Error("can't decrypt");
                     },
-                } as CryptoBackend;
-
+                } as Parameters<MatrixEvent["attemptDecryption"]>[0];
                 await mxEvent.attemptDecryption(mockCrypto);
 
                 const { container } = getComponent();