Fix CI s3 api command to fetch latest results (#15687)

An `s3` fetch api seems to be returning incorrectly ordered output, this PR fixes the issue.

Authors:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Ray Douglass (https://github.com/raydouglass)

URL: #15687

ci/cudf_pandas_scripts/pandas-tests/diff.sh

@@ -17,10 +17,8 @@ MAIN_ARTIFACT=$(rapids-s3-path)cuda12_$(arch)_py${PY_VER}.main-${RAPIDS_FULL_VER
 PR_ARTIFACT=$(rapids-s3-path)cuda12_$(arch)_py${PY_VER}.pr-${RAPIDS_FULL_VERSION}-results.json
 
 rapids-logger "Fetching latest available results from nightly"
-aws s3api list-objects-v2 --bucket rapids-downloads --prefix "nightly/" --query "sort_by(Contents[?ends_with(Key, '_py${PY_VER}.main-${RAPIDS_FULL_VERSION}-results.json')], &LastModified)[::-1].[Key]" --output text > s3_output.txt
-
-read -r COMPARE_ENV < s3_output.txt
-export COMPARE_ENV
+aws s3api list-objects-v2 --bucket rapids-downloads --prefix "nightly/" --query "sort_by(Contents[?ends_with(Key, '_py${PY_VER}.main-${RAPIDS_FULL_VERSION}-results.json')], &LastModified)[::].[Key]" --output text  | tee s3_output.txt
+COMPARE_ENV=$(tail -n 1 s3_output.txt)
 rapids-logger "Latest available results from nightly: ${COMPARE_ENV}"
 
 aws s3 cp "s3://rapids-downloads/${COMPARE_ENV}" main-results.json