Refactor test code for readability

[bowenxia]

What changed?

• Refactor test code of pinot_query_validator for readability:
  • deleted all the double quotes backslash inside of strings, and quoted the entire string with ``.

Why?
for readability

How did you test it?
unti test

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.20%. Comparing base (71cf16a) to head (ddb6731).
Report is 5 commits behind head on master.

Additional details and impacted files

see 17 files with indirect coverage changes

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