Overnight benchmarks - find a valid issue assignee (#4627)

* Overnight benchmarks find a valid issue assignee.

* Overnight benchmarks safer check for a valid issue assignee.

Author: trexfeathers

.github/workflows/benchmark.yml

@@ -81,7 +81,16 @@ jobs:
             do
               commit="${commit_file%.*}"
               pr_number=$(git log "$commit"^! --oneline | grep -o "#[0-9]*" | tail -1 | cut -c 2-)
-              assignee=$(gh pr view $pr_number --json author -q '.["author"]["login"]' --repo $GITHUB_REPOSITORY)
+              author=$(gh pr view $pr_number --json author -q '.["author"]["login"]' --repo $GITHUB_REPOSITORY)
+              merger=$(gh pr view $pr_number --json mergedBy -q '.["mergedBy"]["login"]' --repo $GITHUB_REPOSITORY)
+              # Find a valid assignee from author/merger/nothing.
+              if curl -s https://api.github.com/users/$author | grep -q "login"; then
+                assignee=$author
+              elif curl -s https://api.github.com/users/$merger | grep -q "login"; then
+                assignee=$merger
+              else
+                assignee=""
+              fi
               title="Performance Shift(s): \`$commit\`"
               body="
           Benchmark comparison has identified performance shifts at commit \