ci: Fix Postgres and MySQL tests (no-changelog) (#8106)

This role query works for sqlite but [fails for Postgres and
MySQL](https://github.com/n8n-io/n8n/actions/runs/7269009778/job/19805986017),
so generalize by adding alias and accounting for count possibly being
`string` in the resulting rows.

Run in progress: https://github.com/n8n-io/n8n/actions/runs/7275986797

.github/workflows/ci-postgres-mysql.yml

@@ -6,7 +6,7 @@ on:
   workflow_dispatch:
   pull_request:
     paths:
-      - packages/cli/src/databases/migrations/**
+      - packages/cli/src/databases/**
 
 concurrency:
   group: db-${{ github.event.pull_request.number || github.ref }}
@@ -65,7 +65,7 @@ jobs:
 
       - name: Test MySQL
         working-directory: packages/cli
-        run: DB_TABLE_PREFIX=test_ pnpm test:mysql --runInBand
+        run: pnpm test:mysql
 
   postgres:
     name: Postgres
@@ -98,7 +98,7 @@ jobs:
 
       - name: Test Postgres
         working-directory: packages/cli
-        run: DB_POSTGRESDB_SCHEMA=alt_schema DB_TABLE_PREFIX=test_ pnpm test:postgres --runInBand
+        run: pnpm test:postgres
 
   notify-on-failure:
     name: Notify Slack on failure