Fixes accessibility behavior of Watching, Staring and Fork buttons (#22634)

Add tabindex to buttons of repository views.

templates/repo/header.tmpl

@@ -68,7 +68,7 @@
 					{{end}}
 					<form method="post" action="{{$.RepoLink}}/action/{{if $.IsWatchingRepo}}un{{end}}watch?redirect_to={{$.Link}}">
 						{{$.CsrfTokenHtml}}
-						<div class="ui labeled button{{if not $.IsSigned}} tooltip{{end}}" tabindex="0"{{if not $.IsSigned}} data-content="{{$.locale.Tr "repo.watch_guest_user"}}" data-position="top center"{{end}}>
+						<div class="ui labeled button{{if not $.IsSigned}} tooltip{{end}}"{{if not $.IsSigned}} data-content="{{$.locale.Tr "repo.watch_guest_user"}}" data-position="top center"{{end}}>
 							<button type="submit" class="ui compact small basic button"{{if not $.IsSigned}} disabled{{end}}>
 								{{if $.IsWatchingRepo}}{{svg "octicon-eye-closed" 16}}{{$.locale.Tr "repo.unwatch"}}{{else}}{{svg "octicon-eye"}}{{$.locale.Tr "repo.watch"}}{{end}}
 							</button>
@@ -80,7 +80,7 @@
 					{{if not $.DisableStars}}
 						<form method="post" action="{{$.RepoLink}}/action/{{if $.IsStaringRepo}}un{{end}}star?redirect_to={{$.Link}}">
 							{{$.CsrfTokenHtml}}
-							<div class="ui labeled button{{if not $.IsSigned}} tooltip{{end}}" tabindex="0"{{if not $.IsSigned}} data-content="{{$.locale.Tr "repo.star_guest_user"}}" data-position="top center"{{end}}>
+							<div class="ui labeled button{{if not $.IsSigned}} tooltip{{end}}"{{if not $.IsSigned}} data-content="{{$.locale.Tr "repo.star_guest_user"}}" data-position="top center"{{end}}>
 								<button type="submit" class="ui compact small basic button"{{if not $.IsSigned}} disabled{{end}}>
 									{{if $.IsStaringRepo}}{{svg "octicon-star-fill"}}{{$.locale.Tr "repo.unstar"}}{{else}}{{svg "octicon-star"}}{{$.locale.Tr "repo.star"}}{{end}}
 								</button>
@@ -100,7 +100,7 @@
 							{{else if and (not $.CanSignedUserFork) (eq (len $.UserAndOrgForks) 0)}}
 								data-content="{{$.locale.Tr "repo.fork_from_self"}}"
 							{{end}}
-						data-position="top center" tabindex="0">
+						data-position="top center">
 							<a class="ui compact{{if $.ShowForkModal}} show-modal{{end}} small basic button"
 								{{if not $.CanSignedUserFork}}
 									{{if gt (len $.UserAndOrgForks) 1}}