Riccardo trying to fix bugs #1475 and #1477 properly

# Execution Plan: Resolving PRs 1477 and 1475

## Background
- **PRs:** [1477 (Postgres)](https://github.com/GoogleCloudPlatform/ruby-docs-samples/pull/1477) and [1475 (MySQL)](https://github.com/GoogleCloudPlatform/ruby-docs-samples/pull/1475)
- **Goal:** Update the `app.yaml` files for the GAE Flex Rails 7 tutorials to use modern Ruby versions (e.g., 3.2 or 3.3) on `ubuntu22`, fixing the "end of support" error described in Issue #1476.
- **Current Proposed Fix in PRs:** Added `runtime_config: operating_system: "ubuntu22"` to `app.yaml`.

## Current Roadblocks / Comments
1. **CI Pipeline Failures:** `glasnt` identified that the oldest tested Ruby version is failing due to issues with built-in Gemfile config versions. They suggested updating the repository's oldest supported testing ruby version.
2. **Deployment Errors:** `bipashant` tested the PR and still received an error: `runtime ruby32 is not selectable with operating system ubuntu22`. This suggests the current patch in the PR is incomplete or incorrectly specifies the GAE Flex environment for newer Rubies.

## Recommended Execution Steps

### Step 1: Fix CI Matrix (Address glasnt's feedback)
- Investigate the central CI configurations (likely in `.kokoro/` or `.github/workflows/`).
- Update the Ruby version matrix to drop unsupported EOL Rubies (like 2.6/2.7/3.0) and include modern versions (3.2 and 3.3).
- Update the oldest tested Ruby to at least 3.1 or 3.2.

### Step 2: Validate GAE Flex Configuration (Address bipashant's feedback)
- Research the exact `app.yaml` syntax required to run Ruby 3.2+ on `ubuntu22` in GAE Flex.
- It likely requires either:
1. Adding a `.ruby-version` file to the directories specifying `3.2.3` (or similar) AND keeping the `operating_system: "ubuntu22"` in `app.yaml`.
2. Specifying `runtime_version` under `runtime_config` within `app.yaml`.
- Deploy locally using `gcloud app deploy` (or dry-run) to a test project to ensure the `INVALID_ARGUMENT` error resolves.

### Step 3: Implement Changes in PRs
- For both `appengine/rails-cloudsql-postgres` and `appengine/rails-cloudsql-mysql`:
- Adjust `app.yaml` based on the successful syntax from Step 2.
- Adding `.ruby-version` if necessary.
- Update `Gemfile`/`Gemfile.lock` to reflect changes if bounded by bundler requirements.
- Commit these changes directly to the respective branches for PR 1477 (`palladius-patch-2`) and PR 1475 (`palladius-patch-1`), or create a new consolidated PR linking both.

### Step 4: Finalize
- Confirm CI passes after adjusting the ruby matrix.
- Reply to reviewers `glasnt` and `bipashant`, requesting re-review.
- Merge the PRs.

Bắt đầu với các cấu hình .kokoro/ hoặc .github/workflows/ và các tệp app.yaml trong appengine/rails-cloudsql-postgres và appengine/rails-cloudsql-mysql. Xác minh cú pháp Ruby và Ubuntu 22 GAE Flex bắt buộc, sau đó chạy CI và sử dụng gcloud app deploy hoặc một dry run để xác nhận lỗi INVALID_ARGUMENT đã được giải quyết cho cả hai mẫu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.