[CI] switch batch jobs to use G4dn.2x instance

[szha]

Description

switch batch jobs to use g4dn.2x instance. the updated job definition reduces allocated memory from 40G to 30G since g4dn.2x has 32G memory

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

• update batch job definition to reduce memory requirement

cc @dmlc/gluon-nlp-team

[codecov]

Codecov Report

Merging #1041 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1041   +/-   ##
=======================================
  Coverage   88.27%   88.27%           
=======================================
  Files          67       67           
  Lines        6254     6254           
=======================================
  Hits         5521     5521           
  Misses        733      733

[mli]

Job PR-1041/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1041/1/index.html