Perform Newest sort type correctly when sorting issues (#30644)

Should resolve #30642.

Before this commit, we were treating an empty `?sort=` query parameter
as the correct sorting type (which is to sort issues in descending order
by their created UNIX time). But when we perform `sort=latest`, we did
not include this as a type so we would sort by the most recently updated
when reaching the `default` switch statement block.

This commit fixes this by considering the empty string, "latest", and
just any other string that is not mentioned in the switch statement as
sorting by newest.

modules/indexer/issues/dboptions.go

@@ -68,7 +68,7 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 	searchOpt.Paginator = opts.Paginator
 
 	switch opts.SortType {
-	case "":
+	case "", "latest":
 		searchOpt.SortBy = SortByCreatedDesc
 	case "oldest":
 		searchOpt.SortBy = SortByCreatedAsc
@@ -86,7 +86,7 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		searchOpt.SortBy = SortByDeadlineDesc
 	case "priority", "priorityrepo", "project-column-sorting":
 		// Unsupported sort type for search
-		searchOpt.SortBy = SortByUpdatedDesc
+		fallthrough
 	default:
 		searchOpt.SortBy = SortByUpdatedDesc
 	}