Change whitelist to allow_list

[karlhigley]

Description

Swaps out whitelist for a better term.

Checklist

• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels

[codecov]

Codecov Report

Merging #3675 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3675   +/-   ##
=======================================
  Coverage   94.79%   94.79%           
=======================================
  Files         184      184           
  Lines       18227    18227           
=======================================
  Hits        17278    17278           
  Misses        949      949           

Impacted Files	Coverage Δ
test/workers/test_base.py	100.00% <100.00%> (ø)
test/workers/test_virtual.py	100.00% <100.00%> (ø)
test/workers/test_websocket_worker.py	100.00% <100.00%> (ø)