fix runner count logic in set_test_package_matrix.sh from adding an a…

…dditional runner (#19620)

* fix runner count logic in set_test_package_matrix.sh from adding an additional runner

* use ceil instead of floor

.github/scripts/set_test_package_matrix.sh

@@ -5,7 +5,13 @@
 set -euo pipefail
 export RUNNER_COUNT=$1
 
+if ((RUNNER_COUNT < 1 ))
+then
+  echo ERROR: RUNNER_COUNT must be greater than zero.
+  exit 1 # terminate and indicate error
+fi
+
 # set matrix var to list of unique packages containing tests
-matrix="$(go list -json="ImportPath,TestGoFiles" ./... | jq --compact-output '. | select(.TestGoFiles != null) | .ImportPath' | shuf | jq --slurp --compact-output '.' | jq --argjson runnercount $RUNNER_COUNT  -cM '[_nwise(length / $runnercount | floor)]'))"
+matrix="$(go list -json="ImportPath,TestGoFiles" ./... | jq --compact-output '. | select(.TestGoFiles != null) | .ImportPath' | shuf | jq --slurp --compact-output '.' | jq --argjson runnercount $RUNNER_COUNT  -cM '[_nwise(length / $runnercount | ceil)]'))"
 
 echo "matrix=${matrix}" >> "${GITHUB_OUTPUT}"