fix(#32667): 🐛 Fixe a keystring misuse and refactor duplicates keystrings (#32668)

- Fixes a translation keystring misuse where the string 'open
milestones' is used in place of 'closed milestones'.
- De-duplicates the use of 'open milesones' and 'closed milestones'
keystrings on the sidebar of an issue, reusing the ones on the issues
filter and action bars.
- Closes #32667

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

options/locale/locale_en-US.ini

@@ -1461,8 +1461,6 @@ issues.new.no_items = No items
 issues.new.milestone = Milestone
 issues.new.no_milestone = No Milestone
 issues.new.clear_milestone = Clear milestone
-issues.new.open_milestone = Open Milestones
-issues.new.closed_milestone = Closed Milestones
 issues.new.assignees = Assignees
 issues.new.clear_assignees = Clear assignees
 issues.new.no_assignees = No Assignees

templates/repo/issue/filter_actions.tmpl

@@ -58,7 +58,7 @@
 				{{end}}
 				{{if .ClosedMilestones}}
 					<div class="divider"></div>
-					<div class="header">{{ctx.Locale.Tr "repo.issues.filter_milestone_open"}}</div>
+					<div class="header">{{ctx.Locale.Tr "repo.issues.filter_milestone_closed"}}</div>
 					{{range .ClosedMilestones}}
 						<div class="item issue-action" data-element-id="{{.ID}}" data-url="{{$.RepoLink}}/issues/milestone">
 							{{.Name}}

templates/repo/issue/sidebar/milestone_list.tmpl

@@ -22,7 +22,7 @@
 				<div class="item clear-selection">{{ctx.Locale.Tr "repo.issues.new.clear_milestone"}}</div>
 				<div class="scrolling menu">
 					{{if $data.OpenMilestones}}
-						<div class="header">{{ctx.Locale.Tr "repo.issues.new.open_milestone"}}</div>
+						<div class="header">{{ctx.Locale.Tr "repo.issues.filter_milestone_open"}}</div>
 						{{range $data.OpenMilestones}}
 							<a class="item muted" data-value="{{.ID}}" href="{{$pageMeta.RepoLink}}/issues?milestone={{.ID}}">
 								{{svg "octicon-milestone" 18}} {{.Name}}
@@ -31,7 +31,7 @@
 					{{end}}
 					{{if and $data.OpenMilestones $data.ClosedMilestones}}<div class="divider"></div>{{end}}
 					{{if $data.ClosedMilestones}}
-						<div class="header">{{ctx.Locale.Tr "repo.issues.new.closed_milestone"}}</div>
+						<div class="header">{{ctx.Locale.Tr "repo.issues.filter_milestone_closed"}}</div>
 						{{range $data.ClosedMilestones}}
 							<a class="item muted" data-value="{{.ID}}" href="{{$pageMeta.RepoLink}}/issues?milestone={{.ID}}">
 								{{svg "octicon-milestone" 18}} {{.Name}}