Fix `mdbook-linkcheck` CI flakiness

[DelevoXDG]

Current State

We're repeatedly encountering issues with mdbook-linkcheck, causing our tests to fail

https://github.com/foundry-rs/starknet-foundry/actions/runs/22404711458/job/64861067151

E.g.

error: Server returned 415 Unsupported Media Type for https://www.starknet.io/cairo-book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#paths-for-referring-to-an-item-in-the-module-tree
   ┌─ testing/running-tests.md:27:30
   │
27 │ By default, any test with an [absolute module tree path](https://www.starknet.io/cairo-book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#paths-for-referring-to-an-item-in-the-module-tree) matching the filter will be run.
   │                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Server returned 415 Unsupported Media Type for https://www.starknet.io/cairo-book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#paths-for-referring-to-an-item-in-the-module-tree

Objective

We should add some retry on our CI, to reduce probability this fails the entire CI

Additional Context

No response