Generate: increase left-padding test atol
# What does this PR do?

As stated in #23437, `GPTBigCode` was failing the left padding test. Upon further investigation:
1. `GPTBigCode` is left padding compatible, it accepts `position_ids` and uses them correctly
2. The test is only failing on CPU
3. The diff extremely small...

...so I've raised `atol` to `1e-7` (instead of the default `1e-8`) 👀 With `1e-7`, we can still detect failing cases, like the ones skipped in #23437 
_The documentation is not available anymore as the PR was closed or merged._