Update link generate-random-numbers-contracts.md

[NikolaiKryshnev]

What changed? Why?
Replaced outdated Supra Oracles link with the current Arbitrum docs link for Supra VRF. The old link was broken.

Notes to reviewers

• Please verify the new link works and points to the correct Supra VRF section.
• Only this reference was updated; others remain valid.

How has it been tested?

• Opened the new link — accessible and correct.
• Checked Markdown rendering — works fine.
• Docs build passes without errors.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1