Fix R package build on CI. (#8445)

Co-authored-by: Hyunsu Cho <chohyu01@cs.washington.edu>

tests/buildkite/build-rpkg-win64-gpu.ps1

@@ -5,12 +5,12 @@ $ErrorActionPreference = "Stop"
 Write-Host "--- Build XGBoost R package with CUDA"
 
 nvcc --version
+$arch_flag = "-DGPU_COMPUTE_VER=75"
+
+bash tests/ci_build/build_r_pkg_with_cuda_win64.sh $Env:BUILDKITE_COMMIT
+if ($LASTEXITCODE -ne 0) { throw "Last command failed" }
+
 if ( $is_release_branch -eq 1 ) {
-  $arch_flag = "-DGPU_COMPUTE_VER=75"
-
-  bash tests/ci_build/build_r_pkg_with_cuda_win64.sh $Env:BUILDKITE_COMMIT
-  if ($LASTEXITCODE -ne 0) { throw "Last command failed" }
-
   Write-Host "--- Upload R tarball"
   Get-ChildItem . -Filter xgboost_r_gpu_win64_*.tar.gz |
   Foreach-Object {