Expire caches after project creation to ensure a consistent state

Closes #14961

app/models/repository.rb

@@ -331,6 +331,8 @@ class Repository
   # Runs code after a repository has been created.
   def after_create
     expire_exists_cache
+    expire_root_ref_cache
+    expire_emptiness_caches
   end
 
   # Runs code just before a repository is deleted.

spec/models/repository_spec.rb

@@ -670,6 +670,19 @@ describe Repository, models: true do
 
       repository.after_create
     end
+
+    it 'flushes the root ref cache' do
+      expect(repository).to receive(:expire_root_ref_cache)
+
+      repository.after_create
+    end
+
+    it 'flushes the emptiness caches' do
+      expect(repository).to receive(:expire_emptiness_caches)
+
+      repository.after_create
+    end
+
   end
 
   describe "#main_language" do