Please define actions workflow permissions

## Workflow permissions improvement

There are **2 workflow files** that are currently lacking explicit permissions

### Affected Workflow Files

The following workflow files need permissions to be explicitly defined:

- [`.github/workflows/go-unit-tests.yml`](https://github.com/github/gh-mysql-conf-diff/blob/main/.github/workflows/go-unit-tests.yml)
- [`.github/workflows/validate-markdown-docs.yml`](https://github.com/github/gh-mysql-conf-diff/blob/main/.github/workflows/validate-markdown-docs.yml)

### Request

Ensure permissions are explicitly defined. Below are Copilot prompts/instructions if you would like Copilot's assistance with addressing this.

## GitHub Copilot Assignment Prompts and Context

**Task**: Add explicit permissions to GitHub Actions workflow files that are currently missing them.

**Scope**: Update the workflow files listed above to include appropriate `permissions:` blocks.

**Analysis Methodology**:
1. **Gather Current State**: Check if the workflow has any existing permissions defined
2. **Inventory Workflow Actions**:
- Actions performed directly by the workflow
- API calls made by the workflow
- External actions included via `uses:` statements
3. **Determine Required Permissions**: Map each action to its minimum required permissions
4. **Synthesize Minimal Permissions**: Create permissions block with only necessary permissions

**Requirements**:
1. Add a `permissions:` block to each workflow file that doesn't have one
2. Start with `contents: read` as the minimum permission
3. Add additional permissions only if the workflow actually needs them based on the actions it performs
4. Place the `permissions:` block at the job level or workflow level as appropriate
5. Ensure the syntax is correct and follows YAML formatting
6. Maintain existing content formatting, including indentation and comments

**Files to modify**: See the list of affected workflow files above.

**Acceptance criteria**:
- [ ] All listed workflow files have explicit permissions defined
- [ ] Permissions follow the principle of least privilege
- [ ] YAML syntax is valid
- [ ] Workflows still function correctly after changes

## Copilot Instructions:

Please create a pull request that adds appropriate `permissions:` blocks to each of the workflow files listed above. Analyze each workflow to determine the minimum permissions required based on the actions it performs, and add only those necessary permissions.

Bắt đầu bằng cách đọc .github/workflows/go-unit-tests.yml và .github/workflows/validate-markdown-docs.yml, sau đó lập danh mục các job và uses: actions của chúng để xác định các quyền tối thiểu cần thiết. Xác thực cấu hình YAML và workflow sau khi thêm các quyền tường minh; được xem là hoàn thành khi cả hai workflow được liệt kê đều định nghĩa quyền theo nguyên tắc đặc quyền tối thiểu và vẫn giữ định dạng hợp lệ.

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