Fix API not persisting pull request unit config when has_pull_requests is not set (#36718)

The `PATCH /api/v1/repos/{owner}/{repo}` endpoint silently ignores pull
request config fields (like `default_delete_branch_after_merge`,
`allow_squash_merge`, etc.) unless `has_pull_requests: true` is also
included in the request body. This is because the entire PR unit config
block was gated behind `if opts.HasPullRequests != nil`.

This PR restructures the logic so that PR config options are applied
whenever the pull request unit already exists on the repo, without
requiring `has_pull_requests` to be explicitly set. A new unit is only
created when `has_pull_requests: true` is explicitly sent.

Fixes https://github.com/go-gitea/gitea/issues/36466
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/convert/repository.go

@@ -118,7 +118,7 @@ func innerToRepo(ctx context.Context, repo *repo_model.Repository, permissionInR
 		allowManualMerge = config.AllowManualMerge
 		autodetectManualMerge = config.AutodetectManualMerge
 		defaultDeleteBranchAfterMerge = config.DefaultDeleteBranchAfterMerge
-		defaultMergeStyle = config.GetDefaultMergeStyle()
+		defaultMergeStyle = config.DefaultMergeStyle
 		defaultAllowMaintainerEdit = config.DefaultAllowMaintainerEdit
 		defaultTargetBranch = config.DefaultTargetBranch
 	}

services/repository/create.go

@@ -386,15 +386,7 @@ func createRepositoryInDB(ctx context.Context, doer, u *user_model.User, repo *r
 				},
 			})
 		case unit.TypePullRequests:
-			units = append(units, repo_model.RepoUnit{
-				RepoID: repo.ID,
-				Type:   tp,
-				Config: &repo_model.PullRequestsConfig{
-					AllowMerge: true, AllowRebase: true, AllowRebaseMerge: true, AllowSquash: true, AllowFastForwardOnly: true,
-					DefaultMergeStyle: repo_model.MergeStyle(setting.Repository.PullRequest.DefaultMergeStyle),
-					AllowRebaseUpdate: true,
-				},
-			})
+			units = append(units, repo_model.DefaultPullRequestsUnit(repo.ID))
 		case unit.TypeProjects:
 			units = append(units, repo_model.RepoUnit{
 				RepoID: repo.ID,