pw_rpc: Fix typing in unaryWait return value in TS client

A branch ensures that a response exists, so it cannot be undefined.

Change-Id: Icac75b680d2eba23f79706f8d0f780544c34afdb
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/231071
Presubmit-Verified: CQ Bot Account <[email protected]>
Owners-Override: Alexei Frolov <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Lint: Lint 🤖 <[email protected]>
Pigweed-Auto-Submit: Alexei Frolov <[email protected]>
Reviewed-by: Wyatt Hepler <[email protected]>

pw_rpc/ts/call.ts

@@ -266,7 +266,7 @@ export class Call {
     if (this.responses.length !== 1) {
       throw Error(`Unexpected number of responses: ${this.responses.length}`);
     }
-    return [this.status!, this.responses.last()];
+    return [this.status!, this.responses.last()!];
   }
 
   protected async streamWait(timeoutMs?: number): Promise<[Status, Message[]]> {