add permission check

Author: wxiaoguang

templates/repo/code/upstream_diverging_info.tmpl

@@ -5,8 +5,10 @@
 		{{$upstreamHtml := HTMLFormat `<a href="%s">%s:%s</a>` $upstreamLink .Repository.BaseRepo.FullName .BranchName}}
 		{{ctx.Locale.TrN .UpstreamDivergingInfo.CommitsBehind "repo.pulls.upstream_diverging_prompt_behind_1" "repo.pulls.upstream_diverging_prompt_behind_n" .UpstreamDivergingInfo.CommitsBehind $upstreamHtml}}
 	</div>
+	{{if .CanWriteCode}}
 	<button class="ui compact green button tw-m-0 link-action" data-url="{{.Repository.Link}}/branches/merge-upstream?branch={{.BranchName}}">
 		{{ctx.Locale.Tr "repo.pulls.upstream_diverging_merge"}}
 	</button>
+	{{end}}
 </div>
 {{end}}