[Backport] [API] Allow only specific Colums to be updated on Issue (#9539) (#9580)

* Fix #9189 - API Allow only specific Colums to be updated on Issue (#9539)

* dont insert "-1" in any case to issue.poster_id

* Make sure API cant override importand fields

* code format

* add Test for IssueEdit

* load milestone and return it on IssueEdit via API

* extend Test for TestAPIEditIssue

* fix TEST

* make sure Poster is loaded

* keep code format on backport as it is

models/fixtures/repository.yml

@@ -547,7 +547,8 @@
   is_private: false
   num_stars: 0
   num_forks: 0
-  num_issues: 0
+  num_issues: 1
+  num_milestones: 1
   is_mirror: false
 
 -