Update `notification_service.py`
# What does this PR do?

While working on CI report with PyTorch `2.0.0`, the first run failed to send the report due to the following problem:

- The original code checked each line in `summary_short.txt` by `if re.search("FAILED", line):`
- We expect such occurrences have 1-1 correspondence in the file `failures_line.txt`
- However, some lines in `summary_short.txt` might have ` FAILED` but not really what we are looking for. For example, some tests in `tests/extended/test_trainer_ext.py` using `execute_subprocess_async` and we get some lines like
  ```
  /transformers/examples/pytorch/translation/run_translation.py FAILED
  ```
- In such cases, we get error `stacktraces.pop(0)` at some point, as there is no more element to pop (`stacktraces`, obtained from `failures_line.txt`)
- **This PR avoids this situation by checking with `if line.startswith("FAILED "):` which should give the desired 1-1 correspondence.**

_The documentation is not available anymore as the PR was closed or merged._