[CI] add integration tests for ragged_tensor

[bojiang]

Description

Motivation and Context

How Has This Been Tested?

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature and improvements (non-breaking change which adds/improves functionality)
• Bug fix (non-breaking change which fixes an issue)
• Code Refactoring (internal change which is not user facing)
• Documentation
• Test, CI, or build

Component(s) if applicable

• BentoService (service definition, dependency management, API input/output adapters)
• Model Artifact (model serialization, multi-framework support)
• Model Server (mico-batching, dockerisation, logging, OpenAPI, instruments)
• YataiService gRPC server (model registry, cloud deployment automation)
• YataiService web server (nodejs HTTP server and web UI)
• Internal (BentoML's own configuration, logging, utility, exception handling)
• BentoML CLI

Checklist:

• My code follows the bentoml code style, both ./dev/format.sh and
  ./dev/lint.sh script have passed
  (instructions).
• My change reduces project test coverage and requires unit tests to be added
• I have added unit tests covering my code change
• My change requires a change to the documentation
• I have updated the documentation accordingly

[codecov]

Codecov Report

Merging #1303 (d05ac62) into master (ec65bf6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1303   +/-   ##
=======================================
  Coverage   67.27%   67.27%           
=======================================
  Files         144      144           
  Lines        9310     9310           
=======================================
  Hits         6263     6263           
  Misses       3047     3047           

Impacted Files	Coverage Δ
bentoml/frameworks/tensorflow.py	81.90% <0.00%> (-0.96%)	⬇️
bentoml/utils/tensorflow.py	76.78% <0.00%> (+0.89%)	⬆️

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