docs: fix license url (MystenLabs#18024)

## Description 

Replaced the url on the doc site with the right one since it goes 404. 

## Test plan 

### How did you test the new or updated feature?

manually check if the link works.

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

docs/site/docusaurus.config.js

@@ -223,7 +223,7 @@ const config = {
           href: "https://sui.io",
         },
         style: "dark",
-        copyright: `© ${new Date().getFullYear()} Sui Foundation | Documentation distributed under <a href="https://github.com/sui-foundation/sui-docs/blob/main/LICENSE">CC BY 4.0</a>`,
+        copyright: `© ${new Date().getFullYear()} Sui Foundation | Documentation distributed under <a href="https://github.com/MystenLabs/sui/blob/main/docs/site/LICENSE">CC BY 4.0</a>`,
       },
       prism: {
         theme: themes.github,