fix: Correct inverted return value in Scrapy scheduler enqueue_request (#794)

## Summary

- The `enqueue_request` method in `ApifyScheduler` was returning
`bool(result.was_already_present)`, which incorrectly returned `True`
for duplicates and `False` for newly enqueued requests
- Per Scrapy's `BaseScheduler` contract, `enqueue_request` should return
`True` when the request was **successfully stored** (new) and `False`
when rejected (duplicate)
- See
https://docs.scrapy.org/en/latest/topics/scheduler.html#scrapy.core.scheduler.BaseScheduler.enqueue_request
- One-line fix: `return not bool(result.was_already_present)`

## Test plan

- [x] CI passes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vdusek

src/apify/scrapy/scheduler.py

@@ -136,7 +136,7 @@ def enqueue_request(self, request: Request) -> bool:
             raise
 
         logger.debug(f'rq.add_request result: {result}')
-        return bool(result.was_already_present)
+        return not bool(result.was_already_present)
 
     def next_request(self) -> Request | None:
         """Fetch the next request from the scheduler.