Translate `library/unittest.po`

This needs to reach 100% translated.

The rendered version of this file will be available at https://docs.python.org/es/3.14/library/unittest.html once translated.
Meanwhile, the English version is shown.

Current stats for library/unittest.po:

• Fuzzy: 37
• Percent translated: 90.0%
• Entries: 506 / 562
• Untranslated: 56

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Remember to follow the steps in our Contributing Guide.

按照 issue 中链接的 Contributing Guide 操作，并打开 library/unittest.po。检查 56 条未翻译条目和 37 条 fuzzy 条目，用西班牙语翻译或验证它们，并确认文件已达到 100% 翻译完成度，然后再检查渲染后的 unittest 文档页面。