Update checkout to v6

Author: NullVoxPopuli

.github/workflows/publish.yml

@@ -10,7 +10,7 @@ on:
       - main
       - master
     paths:
-      - '.release-plan.json'
+      - ".release-plan.json"
 
 concurrency:
   group: publish-${{ github.head_ref || github.ref }}
@@ -26,12 +26,12 @@ jobs:
       attestations: write
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v6
         with:
           node-version: 22
-          registry-url: 'https://registry.npmjs.org'
+          registry-url: "https://registry.npmjs.org"
           cache: pnpm
       - run: pnpm install --frozen-lockfile
       - run: npm install -g npm@latest # ensure that the globally installed npm is new enough to support OIDC