Fix form action template substitutions on admin pages (#11519)

* Fix form action template substitution on admin dashboard

* Fix form action template substitution on admin monitoring page

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/admin/dashboard.tmpl

@@ -15,7 +15,7 @@
 			{{.i18n.Tr "admin.dashboard.operations"}}
 		</h4>
 		<div class="ui attached table segment">
-			<form method="post" action="{{.AppSubUrl}}/admin">
+			<form method="post" action="{{AppSubUrl}}/admin">
 				{{.CsrfTokenHtml}}
 				<table class="ui very basic table">
 					<tbody>

templates/admin/monitor.tmpl

@@ -7,7 +7,7 @@
 			{{.i18n.Tr "admin.monitor.cron"}}
 		</h4>
 		<div class="ui attached table segment">
-			<form method="post" action="{{.AppSubUrl}}/admin">
+			<form method="post" action="{{AppSubUrl}}/admin">
 				{{.CsrfTokenHtml}}
 				<table class="ui very basic striped table">
 					<thead>