Chore: Fix internal sync (#6566)

## Motivation for features / changes
The internal TS compiler does not seem to understand this typing and is
failing to build the project due to this.

Googlers see [this build
error](https://fusion2.corp.google.com/invocations/93bb13a8-2f19-4353-ae39-1fbebcb484a3/targets/%2F%2Fthird_party%2Ftensorboard%2Fwebapp%2Fruns%2Feffects:effects;config=5586cf857573577a6cafd5ec36717fe7433482d93abeca5f0b792636a7fd48dd/log)

Also see [this successful
build](https://fusion2.corp.google.com/invocations/36e64c96-1280-4f5d-89da-bfbd36172401/targets/%2F%2Fthird_party%2Ftensorboard%2Fwebapp%2Fruns%2Feffects:effects)


[go/typescript-g3patterns#tuple-types](http://goto.google.com/typescript-g3patterns#tuple-types)

tensorboard/webapp/runs/effects/runs_effects.ts

@@ -296,7 +296,12 @@ export class RunsEffects {
       this.maybeFetchHparamsMetadata(experimentId),
     ]).pipe(
       map(([runs, metadata]) => {
-        return {fromRemote: true, experimentId, runs, metadata};
+        return {
+          fromRemote: true,
+          experimentId,
+          runs: runs as Run[],
+          metadata: metadata as HparamsAndMetadata,
+        };
       })
     );
   }