Remove pin of outdated R version

[glatterf42]

Today, I was reminded of #479, which recorded some problem of possibly interfering versions 4.2.3 and 4.3.0 of R in our CI test suite. These were encountered in #478, which introduced a workaround by pinning to 4.2.3.

The current release is 4.4.1, so this workaround/pin might be outdated. This PR tries removing the pin to see if our test suite is still working fine with the latest version of R.

How to review

• Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Update tests setup
• [ ] Add, expand, or update documentation. Just CI.
• [ ] Update release notes. Just CI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.9%. Comparing base (080ad2b) to head (d3b366c).
Report is 17 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #545     +/-   ##
=======================================
+ Coverage   98.8%   98.9%   +0.1%     
=======================================
  Files         44      44             
  Lines       4819    4819             
=======================================
+ Hits        4765    4770      +5     
+ Misses        54      49      -5     

see 2 files with indirect coverage changes

[glatterf42]

This is working for now, it seems; let's see if it re-introduces some flakiness.

[khaeru]

LGTM!

For completeness, I updated the PR description to mention the original PR that introduced the pin.