add codetools for vignettes

[ben-schwen]

As shown by CI our images need codetools to build vignettes. Successful run with codetools is here

We could also add it to the docker images but it feels more right to do it here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.97%. Comparing base (291a711) to head (c150fea).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7542   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files          87       87           
  Lines       16733    16733           
=======================================
  Hits        16561    16561           
  Misses        172      172           

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[github-actions]

• HEAD=CI_codetools slower P<0.001 for DT[by,verbose=TRUE] improved in #6296
  

Generated via commit c150fea

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	5 minutes and 6 seconds
Installing different package versions	11 minutes and 0 seconds
Running and plotting the test cases	4 minutes and 2 seconds