Conversion of alter_session to PosixPath is incorrect

[tkilias]

Background

• alter_session contains a string of the form <LANGUAGE_ALIAS>=
• for whatever reason the conversion to a PosixPath works, but is not what is intended here

bucketfs-utils-python/tests/fixtures/upload_language_container_fixture.py

Line 34 in 56a2db5

alter_session = Path(language_container["alter_session"])

Acceptance Criteria

• Remove the conversion to PosixPath for alter session