Add Pytest icon (light and dark variants)

[Edugs94]

📌 Summary

Added the Pytest icon to the collection.

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🧠 Description

I have created the Light and Dark versions of the Pytest icon.

• Created using the bubble aesthetic to match existing icons.
• Verified dimensions are exactly 512x512 px.
• Centered the icon using viewBox adjustment to maintain the correct padding.

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📸 Screenshots / Previews

Light Mode	Dark Mode

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🔍 Checklist

• I’ve added icons to both icons/dark/ and icons/light/ directories
• SVGs are 512x512 and styled consistently with the project’s design
• I’ve tested any code/backend changes locally (if applicable)
• My PR follows the Contributing Guidelines

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🙋‍♂️ Questions

None. Ready for review!

[YuheshPandian]

Thanks a lot for the contribution.