Don't return boolean for oauth on Geo primary

ee/changelogs/unreleased/ag-fix-oauth-app-for-secondary.yml

+---
+title: 'Geo: Fix OAuth failure on primary'
+merge_request: 47178
+author:
+type: fixed

ee/lib/gitlab/geo.rb

@@ -88,7 +88,7 @@ module Gitlab
     end
 
     def self.oauth_authentication
-      return false unless Gitlab::Geo.secondary?
+      return unless Gitlab::Geo.secondary?
 
       self.cache_value(:oauth_application) do
         Gitlab::Geo.current_node.oauth_application || raise(OauthApplicationUndefinedError)

ee/spec/lib/gitlab/geo_spec.rb

@@ -143,6 +143,7 @@ RSpec.describe Gitlab::Geo, :geo, :request_store do
   end
 
   describe '.oauth_authentication' do
+    context 'for Geo secondary' do
       before do
         stub_secondary_node
         stub_current_geo_node(secondary_node)
@@ -151,6 +152,17 @@ RSpec.describe Gitlab::Geo, :geo, :request_store do
       it_behaves_like 'a Geo cached value', :oauth_authentication, :oauth_application
     end
 
+    context 'for Geo primary' do
+      before do
+        stub_current_geo_node(primary_node)
+      end
+
+      it 'returns nil' do
+        expect(described_class.oauth_authentication).to be_nil
+      end
+    end
+  end
+
   describe '.connected?' do
     context 'when there is a database issue' do
       it 'returns false when database connection is down' do