fix(ci): ensure dependencies installed in quality and test jobs

Add 'mix deps.get --only test' to quality and test jobs after
downloading artifacts to ensure dependencies are current and
prevent 'lock mismatch' errors.

Fast when deps cached, but ensures consistency across all jobs.

.forgejo/workflows/build.yaml

@@ -129,6 +129,9 @@ jobs:
         with:
           name: build-artifacts
 
+      - name: Install dependencies
+        run: mix deps.get --only test
+
       - name: Check code formatting
         if: matrix.task == 'format'
         run: mix format --check-formatted
@@ -175,6 +178,9 @@ jobs:
         with:
           name: build-artifacts
 
+      - name: Install dependencies
+        run: mix deps.get --only test
+
       - name: Wait for PostgreSQL
         run: |
           timeout 30 bash -c 'until pg_isready -h postgres -p 5432 -U postgres; do sleep 1; done'