Set is_private in fixtures. (#18868)

Co-authored-by: Lunny Xiao <[email protected]>

Author: KN4CK3R

models/fixtures/repository.yml

@@ -218,6 +218,7 @@
   lower_name: repo15
   name: repo15
   is_empty: true
+  is_private: true
   status: 0
 
 -
@@ -459,6 +460,7 @@
   owner_name: user2
   lower_name: repo20
   name: repo20
+  is_private: true
   num_stars: 0
   num_forks: 0
   num_issues: 0