fix(plugin-multi-tenant): infinite api calling loop on user switch

[r1tsuu]

Previously, using the multi-tenant example you were able to reproduce the following:

• Login as super-admin demo@payloadcms.com demo
• Logout and login as tenant1 tenant1@payloadcms.com demo
• Logout and login as tenant2 tenant2@payloadcms.com demo

You'd see an infinite spam of requests to /tenants/populate-tenant-options because of useEffect in TenantSelectionProvider/index.client.tsx

Why?
Login as Tenant 2 → userChanged=true → syncTenants() fetches data
→ setTenantOptions(new array) → tenantOptions reference changes
→ effect re-runs (tenantOptions in deps) → stale initialValue ≠ cookie
→ syncTenants() again → new array reference again → ∞

This PR makes the setTenantOptions call stable (avoid a new reference when not changed) and removes tenantOptions from the dependency array (the tenant options selector still updates correctly when logging out / logging in as a different user)

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[github-actions]

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