Fix oss key prefix bug in oss_task_handler, alibaba-provider

[EricGao888]

---

Fix bug discussed in #35654

Sorry for the late fix, I was quite busy at that time when the discussion started. But I think it is better late than never : )

In oss_task_handler of alibaba-provider, oss_write() passes the key with prefix into oss_log_exists(), which duplicately adds the same prefix. This PR fixes the bug and related UT cases.

airflow/airflow/providers/alibaba/cloud/log/oss_task_handler.py

Lines 173 to 175 in f411c14

	oss_remote_log_location = f"{self.base_folder}/{remote_log_location}"
	pos = 0
	if append and self.oss_log_exists(oss_remote_log_location):

airflow/airflow/providers/alibaba/cloud/log/oss_task_handler.py

Lines 132 to 139 in f411c14

	def oss_log_exists(self, remote_log_location):
	"""
	Check if remote_log_location exists in remote storage.
	:param remote_log_location: log's location in remote storage
	:return: True if location exists else False
	"""
	oss_remote_log_location = f"{self.base_folder}/{remote_log_location}"

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in newsfragments.

[EricGao888]

Hi @potiuk , could you please help with the review when available? THX