Fix XCom object storage backend path validation

[amoghrajesh]

universal_pathlib releases a 0.3.0 version and that added pathlib_abc==0.5.1 in it, which introduced stricter type checking on Path objects.

The original code was calling is_relative_to() incorrectly on Path objects leading to error:

  Using airflow version from current sources

  providers/common/io/src/airflow/providers/common/io/xcom/backend.py:105: error: Argument 1 to "is_relative_to" of "PurePath" has incompatible type "ObjectStoragePath"; expected "PurePath"  [arg-type]
                  if not Path.is_relative_to(ObjectStoragePath(data), p):
                                             ^~~~~~~~~~~~~~~~~~~~~~~
  providers/common/io/src/airflow/providers/common/io/xcom/backend.py:105: error: Argument 2 to "is_relative_to" of "PurePath" has incompatible type "ObjectStoragePath"; expected "str | PathLike[str]" 
  [arg-type]
                  if not Path.is_relative_to(ObjectStoragePath(data), p):
                                                                      ^
  Found 2 errors in 1 file (checked 3984 source files)

I have changed to call it as an instance method on the ObjectStoragePath object itself.

---

^ 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 airflow-core/newsfragments.