fix: external mysql deploy test

Author: klesh

.github/workflows/deploy-test.yml

@@ -66,7 +66,7 @@ jobs:
           helm install --debug --wait --timeout 2400s deploy-test charts/devlake \
             --set service.uiPort=30000 \
             --set mysql.useExternal=true \
-            --set mysql.externalServer=mysql \
+            --set mysql.externalServer=mysql.default.svc.cluster.local \
             --set lake.encryptionSecret.secret=$(openssl rand -base64 2000 | tr -dc 'A-Z' | fold -w 128 | head -n 1)
 
       - name: Helm install devlake