Allow scalar values for Query::select()

[Tigrov]

Update tests according main PR yiisoft/db#816

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.02%. Comparing base (e1275ac) to head (1b55207).
Report is 1 commits behind head on master.

❗ Current head 1b55207 differs from pull request most recent head fcb65ff. Consider uploading reports for the commit fcb65ff to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #259   +/-   ##
=========================================
  Coverage     98.02%   98.02%           
  Complexity      175      175           
=========================================
  Files            16       16           
  Lines           556      556           
=========================================
  Hits            545      545           
  Misses           11       11           

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