ci(deps): keep docker/login-action on the floating v4 major

Dependabot's group bump narrowed this pin from `@v3` to the exact patch
`@v4.5.2`. Two problems with that. Every other action ref in the repo is
pinned to a floating major (`@vN`) — after the group bump this was the
only exception left. And an exact patch stops fixes inside v4 from
arriving on their own, while making Dependabot open a PR for every
login-action patch release.

`refs/tags/v4` exists and floats, so `@v4` is the same upgrade with the
convention kept. It is not a stale-latest question either: v4.6.0 was
released 2026-07-29, two days before this PR was opened, so the exact
pin was already behind when it landed.

Author: Victor-w-Madeira

.github/workflows/build-ollama-image.yml

@@ -28,7 +28,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
       - name: Log in to ghcr
-        uses: docker/login-action@v4.5.2
+        uses: docker/login-action@v4
         with:
           registry: ghcr.io
           username: ${{ github.actor }}