Apply suggestions from code review

Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Aramis Sennyey <159921952+aramissennyeydd@users.noreply.github.com>

.changeset/cold-boats-sell.md

@@ -1,5 +1,5 @@
 ---
-'@backstage/plugin-auth-backend-module-guest-provider': patch
+'@backstage/plugin-auth-backend-module-guest-provider': minor
 ---
 
 Adds a new guest provider that maps guest users to actual tokens. This also shifts the default guest login to `user:development/guest` to reduce overlap with your production/real data. To change that (or set it back to the old default, use the new `auth.guestEntityRef` config key) like so,

.changeset/selfish-glasses-cheer.md

@@ -1,5 +1,5 @@
 ---
-'@backstage/core-components': minor
+'@backstage/core-components': patch
 ---
 
 `SignInPage`'s `'guest'` provider now supports the `@backstage/plugin-auth-backend-module-guest-provider` package to generate tokens. It will continue to use the old frontend-only auth as a fallback.

packages/core-components/src/layout/SignInPage/guestProvider.tsx

@@ -32,8 +32,8 @@ const getIdentity = async (identity: ProxiedSignInIdentity) => {
     return identityResponse;
   } catch (error) {
     if (
-      error instanceof ResponseError &&
-      error.cause.name === 'NotFoundError'
+      error.name === 'ResponseError' &&
+      (error as ResponseError).cause.name === 'NotFoundError'
     ) {
       return undefined;
     }