git_checkout_pull_request(): pass repo arg to git_branch_exists()

[zkamvar]

I noticed a bug when attempting to check out a pull request programmatically in a repo in a temporary directory. It turned out that the repo argument was not being passed to git_branch_exists. The workaround at the moment, is to run this code in the git directory.

print(tmp <- tempfile())
#> [1] "/var/folders/t2/chsckzh12t38xqwg17xslwr80000gn/T//RtmpCfmpAw/file888d6ffbc3dc"
print(getwd())
#> [1] "/private/var/folders/t2/chsckzh12t38xqwg17xslwr80000gn/T/Rtmpys1Ric/reprex-82ee7ec139de-fussy-agama"
gert::git_clone("https://github.com/r-lib/gert.git", tmp)
gert::git_checkout_pull_request(pr = 227, repo = tmp)
#> Error in libgit2::git_repository_open_ext: could not find repository at '/private/var/folders/t2/chsckzh12t38xqwg17xslwr80000gn/T/Rtmpys1Ric/reprex-82ee7ec139de-fussy-agama'
withr::with_dir(tmp, {
  gert::git_checkout_pull_request(pr = 227)
})
#> Creating new branch: pr/227

^{Created on 2025-07-23 with reprex v2.1.1}