build: Log in to dockerhub for unit test CI

We're being rate limited by dockerhub for pulling too many images in CI.
There isn't a greate solution for caching images for GH actions, but in
theory we should have less strict limits as an authenticated user.

.github/workflows/unit-tests.yml

@@ -73,6 +73,12 @@ jobs:
         run: |
           sudo apt-get update && sudo apt-get install libmysqlclient-dev libxmlsec1-dev lynx
 
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3.3.0
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Start MongoDB
         uses: supercharge/mongodb-github-action@1.11.0
         with:
@@ -197,7 +203,6 @@ jobs:
           to add any missing apps and match the count. for more details please take a look at scripts/gha-shards-readme.md"
           exit 1
 
-
   # This job aggregates test results. It's the required check for branch protection.
   # https://github.com/marketplace/actions/alls-green#why
   # https://github.com/orgs/community/discussions/33579