Use squash merge when promoting stable releases to main

Co-authored-by: jmiller-moko <230051081+jmiller-moko@users.noreply.github.com>

.github/workflows/release_pipeline.yml

@@ -1007,7 +1007,7 @@ else:
             --body "Automated PR created by release pipeline. Version branch is retained by policy." \
             || true
 
-      - name: Attempt to merge PR (best effort)
+      - name: Attempt to merge PR (best effort, squash merge)
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
@@ -1021,7 +1021,7 @@ else:
             exit 1
           fi
 
-          gh pr merge "${PR_NUMBER}" --merge --delete-branch=false \
+          gh pr merge "${PR_NUMBER}" --squash --delete-branch=false \
             || echo "PR merge blocked by branch protection or policy" >> "${GITHUB_STEP_SUMMARY}"
 
       - name: Report run context (always)