build: remove Python 3.8 references

[DawoudSheraz]

Since Python 3.8 has reached the end of life, keeping 3.8 related references in edx-val is not needed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.52%. Comparing base (9846e6c) to head (902ed80).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #537      +/-   ##
==========================================
+ Coverage   94.48%   94.52%   +0.04%     
==========================================
  Files          31       31              
  Lines        3099     3106       +7     
  Branches      173      120      -53     
==========================================
+ Hits         2928     2936       +8     
  Misses        152      152              
+ Partials       19       18       -1     

Flag	Coverage Δ
unittests	94.52% <100.00%> (+0.04%)	⬆️

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[UsamaSadiq]

It would be better to release a new version as well since the support of Python 3.8 is being dropped.

[DawoudSheraz]

It would be better to release a new version as well since the support of Python 3.8 is being dropped.

I will do it in a followup PR.

[DawoudSheraz]

Created #538 for version bump