chore: bump version to 6.0.20

[zsien]

• fix: the text not being vertically centered (linuxdeepin/developer-center#8899)
• fix: incorrect X-Deepin-Vendor check for LauncherItemInfo
• fix: notification record count could be -1

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: zsien

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[zsien]

/integrate

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 检查是否有遗漏的提交信息，例如在合并时是否有遗漏的提交。
• 确认是否有必要的代码注释，以帮助其他开发者理解代码的目的和功能。
• 验证代码中的错误处理和边界情况处理是否充分。
• 检查是否有必要进行版本更新，以及是否遵循了项目的版本控制策略。

是否建议立即修改:

• 是，确保代码的质量和稳定性是非常重要的，应该立即进行修改。

[github-actions[bot]]

AutoIntegrationPr Bot auto integrate with pr url: https://github.com/deepin-community/Repository-Integration/pull/1609 PrNumber: 1609 PrBranch: auto-integration-9542437257

[github-actions[bot]]

TAG Bot

TAG: 6.0.20 EXISTED: yes DISTRIBUTION: unstable

[deepin-bot[bot]]

TAG Bot

New tag: 6.0.20 DISTRIBUTION: unstable Suggest: synchronizing this PR through rebase #373