[CI] Lift timeout on cpu unittest

[chenw23]

Description

Here is a brief statistics of the CI time out occurrences:
Among the 25 most recent CI builds the following CI items has such rate of time out(excluding failures):
cpu-unittest: 45%
master-cpu-unittest: 33%
gpu-integration: 0%
gpu-unittest: 0%
master-gpu-doc: 0%
master-gpu-integration: 0%
master-gpu-unittest: 0%

Therefore, I am lifting the time out settings for cpu-unittest and master-cpu-unittest so that they can provide steady performance even on peak hours.

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

cc @dmlc/gluon-nlp-team

[mli]

Job PR-1216/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1216/1/index.html

[codecov]

Codecov Report

Merging #1216 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1216   +/-   ##
=======================================
  Coverage   87.42%   87.42%           
=======================================
  Files          81       81           
  Lines        7347     7347           
=======================================
  Hits         6423     6423           
  Misses        924      924