Test preview against the docs-base image from grafana/website#32512

Point the caller at this branch's reusable workflow and pull the
development docs-base image published from the website PR, so the
preview exercises the redirects manifest path instead of the alias
scraping fallback.

The build-website job logs in to GAR when the image comes from
us-docker.pkg.dev, which requires id-token permission from callers.

Revert the caller ref and image pin to main and nightly before merge.

Signed-off-by: Jack Baldry <jack.baldry@grafana.com>

Author: jdbaldry

.github/workflows/deploy-pr-preview.yml

@@ -13,7 +13,8 @@ on:
 
 jobs:
   deploy-pr-preview:
-    uses: grafana/writers-toolkit/.github/workflows/deploy-preview.yml@main # zizmor: ignore[unpinned-uses] It's a protected branch in the same repository.
+    # TODO: revert to @main before merge, iterating on the reusable workflow in this branch.
+    uses: grafana/writers-toolkit/.github/workflows/deploy-preview.yml@jdb/deploy-preview # zizmor: ignore[unpinned-uses] It's a branch in the same repository.
     if: "!github.event.pull_request.head.repo.fork"
     permissions:
       contents: read # Clone repository.
@@ -23,7 +24,9 @@ jobs:
     with:
       branch: ${{ github.head_ref }}
       event_number: ${{ github.event.number }}
-      image: grafana/docs-base:nightly
+      # TODO: revert to grafana/docs-base:nightly before merge, testing the
+      # docs-base image from grafana/website#32512.
+      image: us-docker.pkg.dev/grafanalabs-dev/docker-website-dev/docs-base:0ca6ae60009434fe9a77e3adad6ed507c9c75e23
       repo: writers-toolkit
       sha: ${{ github.event.pull_request.head.sha }}
       sources: |

.github/workflows/deploy-preview.yml

@@ -126,10 +126,17 @@ jobs:
       website_directory: ${{ steps.preview-paths.outputs.website_directory != '' && steps.preview-paths.outputs.website_directory || env.WEBSITE_DIRECTORY }}
     permissions:
       contents: read # Clone repositories.
+      id-token: write # Log in to GAR to pull development docs-base images.
       pull-requests: read # `gh pr checkout` in deploy-preview/build queries the pullRequests GraphQL API.
     if: github.event.action == 'opened' || github.event.action == 'synchronize'
     runs-on: ubuntu-latest
     steps:
+      - name: Log in to GAR
+        if: startsWith(inputs.image, 'us-docker.pkg.dev/')
+        uses: grafana/shared-workflows/actions/login-to-gar@12c87e5aa323694c820c1ff3d8e47e8237e05136 # login-to-gar/v1.0.2
+        with:
+          registry: us-docker.pkg.dev
+
       - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
         if: inputs.website_directory
         with: