Guard github name resolver against empty organization

When a GitHub access-source connector has no organization configured
yet (user finished OAuth but abandoned the picker), the source-name
worker called https://api.github.com/orgs/ and got a 404 every 10
seconds, flooding logs. All other picker resolvers (sentry, gitlab,
bitbucket, heroku, asana, netlify, clickup, vercel) short-circuit to
("", nil) for empty settings -- this aligns github with them so the
worker falls into its existing "empty instance name -> mark synced
with generic name" branch instead of retrying forever.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/accessreview/drivers/name_resolver.go

@@ -552,6 +552,10 @@ func NewGitHubNameResolver(httpClient *http.Client, org string) NameResolver {
 }
 
 func (r *githubNameResolver) ResolveInstanceName(ctx context.Context) (string, error) {
+	if r.org == "" {
+		return "", nil
+	}
+
 	endpoint, err := url.JoinPath("https://api.github.com", "orgs", url.PathEscape(r.org))
 	if err != nil {
 		return "", fmt.Errorf("cannot build github organization URL: %w", err)