fix(ci): keep the checkout token out of the published image

actions/checkout@v5 stored the job's GitHub token in .git/config, and
the image copies .git, so published images contained it. Use checkout
v7 with persist-credentials: false.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/release-please.yml

@@ -32,7 +32,9 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
 
       - uses: docker/login-action@v3
         with: