Add test coverage for postgres upgrade on macOS

🎪 Theme

gdk-reliability

📜 Description

During upgrade effort of Postgres 16, a macOS issue was identified which our current testing setup was not able to detect due to the fact that tests are executed using Linux runners.

Since we're a mac-centric company and PG upgrade is frequently occurring, this represents a high risk gap in our GDK test coverage that directly impacts developer productivity and reliability.

🎯 Success Metrics & KPIs

Primary KPIs:

• Test Coverage: Achieve 100% macOS test coverage for Postgres operations (currently 0%)
• Issue Prevention: Reduce macOS-specific Postgres issues by 90% (baseline: 3 issues in Q2 2025)

Secondary KPIs:

• Developer Experience: Reduce macOS setup failures from Postgres issues by 80%
• Release Confidence: Enable same-day Postgres upgrades for macOS users (currently requires hotfixes)

🤝 Acceptance Criteria

• Postgres Fresh Install Testing
  • macOS CI job validates fresh Postgres installation
  • Test covers all supported macOS versions (latest 2 major versions)
  • Validates installation success rate >95%
• Postgres Upgrade Testing
  • macOS CI job tests upgrade path from N-1 to N version
  • Migration validation with real GDK data
  • Rollback scenario testing
• CI Integration
  • Tests run on every MR affecting Postgres configuration
  • Results block merge if macOS compatibility fails
  • Test execution time <45 minutes

💡 Proposal

Implement dedicated macOS runners for Postgres testing with:

1. Matrix testing across supported macOS versions
2. Automated upgrade/downgrade scenarios
3. Failure notification system

🚫 Blockers

• macOS runner availability/cost approval
• Test data migration strategy definition

Out of scope

• Performance regression testing will be addressed separately