Simplify find config

[MichaelChirico]

Feeds into #2177

I found the structure of the while() loop confusing, it took me quite some time to figure out it's checking both ${PATH}/.lintr and ${PATH}/.github/linters/.lintr on each pass.

I hope this rewrite makes what's going on much clearer. It will also make it trivial to extend for #2177 to also check for .lintr.R.

[codecov-commenter]

Codecov Report

Merging #2205 (774ffb9) into main (2a5e4ab) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 774ffb9 differs from pull request most recent head 1689bce. Consider uploading reports for the commit 1689bce to get more accurate results

@@           Coverage Diff           @@
##             main    #2205   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files         113      113           
  Lines        5161     5161           
=======================================
  Hits         5143     5143           
  Misses         18       18           

Files Changed	Coverage Δ
R/settings_utils.R	100.00% <100.00%> (ø)

[AshesITR]

This can be avoided because file.exists() is vectorized.
Not sure if faster, we should check:

file_exists <- file.exists(files)
if (any(file_exists)) {
  files[which.max(file_exists)]
} else {
  NULL
}

[MichaelChirico]

that's the #2204 TODO -- I wanted to punt on that for now :)