[link-validator] Missing file context-api.md (#637)

* [link-validator] Missing file context-api.md

Hello,

There is a note, with a broken reference link.

| Note: This command lets automation verify that the
|    [context api](https://github.com/fedidcg/FedCM/blob/main/proposals/context-api.md)
|    was applied properly

I searched inside the repo and could not find it.

I am proposing to remove it or feel free to modify the PR.

Thanks,

Simone

P.S. this should be the last check for publication in `/TR`

* Update index.bs

correct link

* Update index.bs

QA

spec/index.bs

@@ -2415,8 +2415,8 @@ The [=remote end steps=] are:
 </figure>
 
 Note: This command lets automation verify that the
-    [context api](https://github.com/fedidcg/FedCM/blob/main/proposals/context-api.md)
-    was applied properly
+  [context api](#dom-identitycredentialrequestoptions-context)
+     was applied properly
 
 The [=remote end steps=] are: