Bump R version dependency to 3.5.0

[MichaelChirico]

2018... a lifetime ago :)

[github-actions]

• HEAD=r350 stopped early for isoweek improved in #7144
• HEAD=r350 slower P<0.001 for memrecycle regression fixed in #5463
  

Generated via commit 907c913

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

Task	Duration
R setup and installing dependencies	2 minutes and 59 seconds
Installing different package versions	45 seconds
Running and plotting the test cases	4 minutes and 23 seconds

[jangorecki]

Ubuntu LTS gets up to 15 years of support so there is a good reasons to hold to older R but I think we all want refcnt

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.97%. Comparing base (a29c209) to head (907c913).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7515   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files          87       87           
  Lines       16740    16741    +1     
=======================================
+ Hits        16568    16569    +1     
  Misses        172      172           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.