fix: use TCP health check and retry loop for MySQL readiness in CI

The previous health check used 'mysqladmin ping -h localhost' which
connects via Unix socket inside the container. This reports healthy
before MySQL's TCP listener is ready, causing 'Lost connection to
MySQL server at reading initial communication packet' when the
Initialize database step attempts a TCP connection.

Changes:
- Health check now uses --protocol=tcp (127.0.0.1) to verify TCP
  listener is up, not just the socket
- Initialize database step adds a TCP retry loop (up to 20 attempts,
  2s sleep) to handle any remaining race condition between health
  check and host-side port availability

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Pierre-Luc Gagné

.github/workflows/ci.yml

@@ -76,7 +76,7 @@ jobs:
             -e MYSQL_DATABASE=ds_mysql_test \
             -e MYSQL_USER=ds_mysql_test_user \
             -e MYSQL_PASSWORD=ds_mysql_test_password \
-            --health-cmd="mysqladmin ping -h localhost" \
+            --health-cmd="mysqladmin ping -h 127.0.0.1 --protocol=tcp" \
             --health-interval=5s \
             --health-timeout=10s \
             --health-retries=10 \
@@ -103,6 +103,20 @@ jobs:
       - name: Initialize database
         run: |
           sudo apt-get install -y mysql-client
+          echo "Waiting for TCP connection on port $DS_MYSQL_TEST_PORT..."
+          for i in $(seq 1 20); do
+            if mysql -h 127.0.0.1 -P "$DS_MYSQL_TEST_PORT" -u root -proot \
+                --connect-timeout=5 -e "SELECT 1" > /dev/null 2>&1; then
+              echo "TCP connection established"
+              break
+            fi
+            if [ "$i" = "20" ]; then
+              echo "MySQL TCP port did not become available in time"
+              exit 1
+            fi
+            echo "Waiting for TCP... ($i/20)"
+            sleep 2
+          done
           mysql -h 127.0.0.1 -P "$DS_MYSQL_TEST_PORT" -u root -proot \
             < tests/integration/docker/init-db.sql