fix(core): check ngDevMode for undefined (#60565)

This adds a check to "toSignal" whether ngDevMode is not undefined as this can happen for some MFE applications.

PR Close #60565

packages/core/rxjs-interop/src/to_signal.ts

@@ -134,7 +134,8 @@ export function toSignal<T, U = undefined>(
   source: Observable<T> | Subscribable<T>,
   options?: ToSignalOptions<T | U> & {initialValue?: U},
 ): Signal<T | U> {
-  ngDevMode &&
+  typeof ngDevMode !== 'undefined' &&
+    ngDevMode &&
     assertNotInReactiveContext(
       toSignal,
       'Invoking `toSignal` causes new subscriptions every time. ' +