fix(ci/check-size): use latest non-merge commit

We were previously using the merge commit as the baseline, leading to
all commits from the pull request being rebased, rather than just the
latest commit.

Signed-off-by: Prajwal S N <prajwalnadig21@gmail.com>

.github/workflows/check-size.yml

@@ -23,4 +23,5 @@ jobs:
     - name: Configure base branch without switching current branch
       run: git fetch origin ${GITHUB_BASE_REF}:${GITHUB_BASE_REF}
     - name: Compare binary size change across each commit
-      run: git rebase -v ${GITHUB_BASE_REF}^ -x test/check-size.sh
+      # Use the last non-merge commit from the base branch as the baseline
+      run: git rebase -v $(git rev-list --no-merges -n 1 ${GITHUB_BASE_REF})^ -x test/check-size.sh