Replace GetOption with GetOption1

[aitap]

As of r87874 we get:

  Found non-API calls to R: ‘LEVELS’, ‘OBJECT’, ‘Rf_GetOption’,
    ‘Rf_isFrame’, ‘SETLENGTH’, ‘SET_GROWABLE_BIT’, ‘SET_TRUELENGTH’,
    ‘TRUELENGTH’

GetOption1() has been available since R-2.13, and GetOption() has been ignoring its second argument for a long time, so there's no portability cost.

See also: #6180

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.59%. Comparing base (b0a17dd) to head (fe15955).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6849      +/-   ##
==========================================
- Coverage   98.60%   98.59%   -0.02%     
==========================================
  Files          79       79              
  Lines       14657    14661       +4     
==========================================
+ Hits        14453    14455       +2     
- Misses        204      206       +2     

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[github-actions]

Generated via commit fe15955

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

Task	Duration
R setup and installing dependencies	4 minutes and 28 seconds
Installing different package versions	8 minutes and 23 seconds
Running and plotting the test cases	2 minutes and 31 seconds