docs: correct the spelling mistake in observables error handling code (#36437)

This commit fixes a spelling error in the word error in the
observables.md guide. It is currently
spelled errror  and the mistake is not intentional.

PR Close #36437

aio/content/guide/observables.md

@@ -112,7 +112,7 @@ Because observables produce values asynchronously, try/catch will not effectivel
 <code-example>
 myObservable.subscribe({
   next(num) { console.log('Next num: ' + num)},
-  error(err) { console.log('Received an errror: ' + err)}
+  error(err) { console.log('Received an error: ' + err)}
 });
 </code-example>