chore: add pre-merge check for newline in perf-changelog.yaml (#579)

* chore: add pre-merge check for newline in perf-changelog.yaml

Add a validation step in run-sweep.yml that ensures perf-changelog.yaml
ends with a newline character. This prevents negative diff issues in
subsequent PRs when the file is appended to.

Closes #578

Co-authored-by: Cameron Quilici <cquil11@users.noreply.github.com>

* test

* change logic of newline check

* trigger test check

* remove test perf changelog

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Cameron Quilici <cquil11@users.noreply.github.com>

Author: cquil11

.github/workflows/run-sweep.yml

@@ -22,6 +22,21 @@ on:
             - "perf-changelog.yaml"
 
 jobs:
+    check-newline:
+        runs-on: ubuntu-latest
+        if: github.event_name == 'pull_request' && !github.event.pull_request.draft
+        steps:
+            - name: Checkout code
+              uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+            - name: Check perf-changelog.yaml ends with newline
+              run: |
+                  if [ -n "$(tail -c 1 perf-changelog.yaml)" ]; then
+                      echo "::error::perf-changelog.yaml must end with a newline character"
+                      echo "Please add a newline at the end of the file to avoid diff issues in subsequent PRs."
+                      exit 1
+                  fi
+
     setup:
         runs-on: ubuntu-latest
         if: >-