[#10] Update docker github action references

Before this commit, we got the error message in our builds:

```
Node.js 16 actions are deprecated. Please update the following actions
to use Node.js 20:
docker/login-action@65b78e6,
docker/metadata-action@9ec57ed,
docker/build-push-action@f2a1d5e. For
more information see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.
```

Apparently, even the GitHub Docs itself are outdated for the last 5
months.

After visiting all the action's versions, I've pinned it to the freshest
versions.

.github/workflows/main.yml

@@ -36,7 +36,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Log in to the Container registry
-        uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1
+        uses: docker/login-action@v3.0.0
         with:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.actor }}
@@ -47,12 +47,12 @@ jobs:
       # However the tags are totally unusable for our case
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@9ec57ed1fcdbf14dcef7dfbe97b2010124a938b7
+        uses: docker/metadata-action@v5.5.1
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
 
       - name: Build and push Docker image
-        uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
+        uses: docker/build-push-action@v5.1.0
         with:
           context: ci
           file: ci/Dockerfile.${{ matrix.distro }}