Add a couple of linkcheck exceptions:

Addresses:
```

Server returned 500 Internal Server Error for https://github.com/rust-lang/rust/pulls?q=is%3Apr+label%3AS-inactive+is%3Aclosed
Server returned 401 Unauthorized for https://objects.githubusercontent.com/github-production-release-asset-2e65be/343907537/60cd5880-7b81-11eb-9502-68d5f473ebe2?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=releaseassetproduction%2F20241103%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20241103T085906Z&X-Amz-Expires=300&X-Amz-Signature=e532fd7d2bd271f12988982bc8e5a47a0f966b40452b55d444bbb74292ac1fb1&X-Amz-SignedHeaders=host&response-content-disposition=attachment%3B%20filename%3Drustc.generic.wpaProfile&response-content-type=application%2Foctet-stream
Server returned 500 Internal Server Error for https://github.com/rust-lang/rust/pulls?q=is%3Apr+label%3AS-inactive
```

book.toml

@@ -43,8 +43,14 @@ exclude = [
     "objects\\.githubusercontent\\.com",
     # The bug listing URL works only if an user is logged in, otherwise one gets 404.
     "github\\.com/issues\\?",
+    # Similarly 500 is sometimes returned here.
+    "github\\.com/rust-lang/rust/pulls\\?",
+    # 401 is returned here for unknown reason
+    "github\\.com/wesleywiser/rustc-bootstrap-wpa-analysis",
     # Handle: connection closed before message completed
     "microsoft\\.com/en-us/research/publication/",
+    # 500 is returned for HEAD request
+    "code\\.visualstudio\\.com/docs/editor/tasks",
 ]
 cache-timeout = 86400
 warning-policy = "error"