enable and migrate test_all.py to python 3

Description

as described. `test_all.py` never ran on Python 3 and this PR fixes it.

Assignee

sburch

Reporter

Open Source Pull Request Bot

Labels

URL

Contributor Name

Omar Al-Ithawi

Repo

edx/xblock-free-text-response

Customer

Epic Link

None

OSCM Assignee

None

Platform Map Area (Levels 1 & 2)

None

Platform Map Area (Levels 3 & 4)

None

Blended Hour Utilization Percentage

None

edX Theme

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edX Squad

None

Github Lines Added

23

Github Lines Deleted

49

Priority

Unset