Travis appveyor build less - 2

[jangorecki]

Closes #2743

[jangorecki]

re-running appveyor build due to below error on R-devel.

 Running test id 1651.008      Error: memory exhausted (limit reached?)
  Execution halted

Memory used in this PR is very low: https://gitlab.com/Rdatatable/data.table/-/jobs/63563227/artifacts/file/bus/test-r-release-vanilla/data.table.Rcheck/tests/memtest.png

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@34f90fb). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2761   +/-   ##
=========================================
  Coverage          ?   93.45%           
=========================================
  Files             ?       61           
  Lines             ?    12323           
  Branches          ?        0           
=========================================
  Hits              ?    11516           
  Misses            ?      807           
  Partials          ?        0

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