fix CI warnings

[ben-schwen]

Two small fixes for clang warnings from GLCI

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.85%. Comparing base (1b998b1) to head (4642aa1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7767   +/-   ##
=======================================
  Coverage   98.85%   98.85%           
=======================================
  Files          87       87           
  Lines       17121    17121           
=======================================
  Hits        16925    16925           
  Misses        196      196           

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[github-actions]

• HEAD=clang_warnings much slower for as.data.table.array improved in #7019
• HEAD=clang_warnings slower P<0.001 for DT[by] max regression fixed in #7480
• HEAD=clang_warnings slower P<0.001 for memrecycle regression fixed in #5463
  

Generated via commit 4642aa1

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

Task	Duration
R setup and installing dependencies	6 minutes and 7 seconds
Installing different package versions	11 minutes and 33 seconds
Running and plotting the test cases	5 minutes and 17 seconds