[CI] add license checker

[szha]

Description

add license checker

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)

Changes

• add license checker to CI

[codecov]

Codecov Report

❗ No coverage uploaded for pull request head (rat@b281763). Click here to learn what that means.
The diff coverage is n/a.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9d069d3). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #804   +/-   ##
=========================================
  Coverage          ?   90.38%           
=========================================
  Files             ?       66           
  Lines             ?     6378           
  Branches          ?        0           
=========================================
  Hits              ?     5765           
  Misses            ?      613           
  Partials          ?        0

[mli]

Job PR-804/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/1/index.html

[mli]

Job PR-804/2 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/2/index.html

[mli]

Job PR-804/3 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/3/index.html

[mli]

Job PR-804/4 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/4/index.html

[mli]

Job PR-804/5 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/5/index.html

[mli]

Job PR-804/6 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-804/6/index.html