Fix typo in findBy description in testing.mdx (#1377)

Author: H7GhosT

src/routes/guides/testing.mdx

@@ -194,7 +194,7 @@ The prefixes (`get`, `query`, and `find`) and the middle portion (`By` and `AllB
 - **getAllBy**: synchronous, throws if not found, returns array of matches
 - **queryBy**: synchronous, null if not found, error if more than 1 matches
 - **queryAllBy**: synchronous, returns array of zero or more matches
-- **findBy**: asynchronous, rejected if not found within 1000ms or more than 1 matches, resolves wth element if found
+- **findBy**: asynchronous, rejected if not found within 1000ms or more than 1 matches, resolves with element if found
 - **findAllBy**: asynchronous, rejected if not found within 1000ms, resolves with array of one or more element(s)
 
 By default, queries should start with `get...`.