Fix exporting POSTGRES_TEST_DSN for CI

Author: kthota-g

.github/workflows/unit-tests.yml

@@ -35,7 +35,7 @@ jobs:
         run: |
           sudo apt-get update && sudo apt-get install -y postgresql-client
           PGPASSWORD=postgres psql -h localhost -p 5432 -U postgres -d a2a_test -f ${{ github.workspace }}/tests/docker/postgres/init.sql
-          export POSTGRES_TEST_DSN="postgresql+asyncpg://postgres:postgres@localhost:5432/a2a_test"
+          echo "POSTGRES_TEST_DSN=postgresql+asyncpg://postgres:postgres@localhost:5432/a2a_test" >> $GITHUB_ENV
 
       - name: Install uv
         uses: astral-sh/setup-uv@v6