Fix CTE query expressions

[Tigrov]

Update tests according to yiisoft/db#761

[what-the-diff]

PR Summary

• Improved Code Syntax in QueryBuilderTest
  In the testing file named QueryBuilderTest.php, there was a tricky syntax issue. The alias terms we use for tables, specifically a1 and a2, were creating confusion. To solve this, they were wrapped with special characters called backticks. This small change helps eliminate any uncertainty the computer may have when reading our code. It ensures our tests run as intended, keeping our software reliable.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (1b375d2) 98.47% compared to head (b71c6e2) 98.47%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #274   +/-   ##
=========================================
  Coverage     98.47%   98.47%           
  Complexity      343      343           
=========================================
  Files            19       19           
  Lines          1046     1046           
=========================================
  Hits           1030     1030           
  Misses           16       16           

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