Make persist-credentials explicit in dedupe checkout

`actions/checkout` has `persist-credentials: true` as its default, but
that default is the load-bearing part of how the later `git push`
authenticates — it's what writes the token into .git/config's
http.extraheader. Making it explicit so a reader of the YAML can see
the mechanism without having to know the action's defaults.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/dependabot-dedupe.yml

@@ -44,8 +44,11 @@ jobs:
           ref: ${{ github.head_ref }}
           # Persist this token in .git/config's http.extraheader so the
           # later `git push` authenticates as the PAT. That's what makes
-          # the dedupe commit trigger CI.
+          # the dedupe commit trigger CI. `persist-credentials: true` is
+          # the checkout default — made explicit here so the mechanism
+          # is visible from the YAML instead of implicit in the action.
           token: ${{ secrets.DEPENDABOT_DEDUPE_TOKEN }}
+          persist-credentials: true
       - uses: pnpm/action-setup@v6
       - uses: actions/setup-node@v6
         with: