r-test fail after "Polars: add `make_expr_col`" merged to main

[mccalluc]

The PR #797 seemed to pass tests but the last run on main failed: https://github.com/opendp/opendp/actions/runs/8818070272/job/24233270642

``` ── R CMD check results ─────────────────────────────────────── opendp 0.9.2 ──── Duration: 1m 21.2s ❯ checking whether package ‘opendp’ can be installed ... [43s/44s] WARNING See below... ❯ checking for hidden files and directories ... NOTE Found the following hidden files and directories: .lintr These were most likely included in error. See section ‘Package structure’ in the ‘Writing R Extensions’ manual. ❯ checking installed package size ... NOTE installed size is 1166.1Mb sub-directories of 1Mb or more: libs 1165.4Mb ❯ checking top-level files ... NOTE Non-standard files/directories found at top level: ‘_pkgdown.yml’ ‘opendp.Rproj’ ‘pkgdown’ ❯ checking Rd files ... NOTE checkRd: (-1) binary_search.Rd:14: Lost braces; missing escapes or markup? 14 | \item{.T}{type of argument to \code{predicate}, one of {float, int}} | ^ checkRd: (-1) binary_search_chain.Rd:18: Lost braces; missing escapes or markup? 18 | \item{.T}{type of argument to \code{make_chain}, one of {float, int}} | ^ checkRd: (-1) binary_search_param.Rd:18: Lost braces; missing escapes or markup? 18 | \item{.T}{type of argument to \code{make_chain}, one of {float, int}} | ^ ❯ checking compilation flags in Makevars ... NOTE Package has both ‘src/Makevars.in’ and ‘src/Makevars’. Installation with --no-configure' is unlikely to work. If you intended ‘src/Makevars’ to be used on Windows, rename it to ‘src/Makevars.win’ otherwise remove it. If ‘configure’ created ‘src/Makevars’, you need a ‘cleanup’ script. 0 errors ✔ | 1 warning ✖ | 5 notes ✖ Error: Error: R CMD check found WARNINGs ```

Having some trouble reading the log:

checking whether package ‘opendp’ can be installed ... [43s/44s] WARNING
  See below...

but I'm not sure which of the lines below it's actually referring to.

Also not sure why this didn't show up the PR before merge.