Confusing UI states when "auth.accessTokens" is set to "none"

Created by: lguychard

• Sourcegraph version: 3.4.1

1. As a site admin, set "auth.accessTokens" to { "allow": "none" } in site configuration.
2. Navigate to /site-admin/tokens
3. Witness "Generate access token" button is present:

4. Click "Generate access token"
5. Witness 404:

I would expect the "Generate access token" button not to be rendered, or to be greyed out. I would also expect the /site-admins/tokens to mention that access token creation is disabled through site configuration.