feat(Tax Docs): Added Portugal and Spain tax docs (#17513)

## DESCRIBE YOUR PR
Added 2026 Portugal and Spain tax docs

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## PRE-MERGE CHECKLIST

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- [ ] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
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Co-authored-by: Shannon Anahata <shannonanahata@gmail.com>

Author: sfanahata

docs/security-legal-pii/security/tax-documents.mdx

@@ -10,6 +10,8 @@ Below you'll find Sentry's tax documents, including the tax residency certificat
 - [W9 CY2025](/pdfs/2025_W9.pdf)
 - [W9 CY2024](/pdfs/W-9-2024-Functional-Software-Inc-signed-rev-March-2024.pdf)
 - [Tax Residency Certificate CY2026 (General Version)](/pdfs/Tax_residency_certificate_CY2026.pdf)
+- [Tax Residency Certificate CY2026 (Portugal)](/pdfs/Tax_residency_certificate_CY2026_Portugal.pdf)
+- [Tax Residency Certificate CY2026 (Spain)](/pdfs/Tax_residency_certificate_CY2026_Spain.pdf)
 - [Tax Residency Certificate CY2025 (General Version)](/pdfs/Tax_residency_certificate_CY2025.pdf)
 - [Tax Residency Certificate CY2024 (General Version)](/pdfs/Tax_residency_certificate_CY2024.pdf)
 - [Tax Residency Certificate CY2023 (General Version)](/pdfs/2023-Form-6166_general.pdf)