enable staticcheck QFxxxx rules (#34064)

routers/web/repo/compare.go

@@ -938,9 +938,10 @@ func ExcerptBlob(ctx *context.Context) {
 				RightHunkSize: rightHunkSize,
 			},
 		}
-		if direction == "up" {
+		switch direction {
+		case "up":
 			section.Lines = append([]*gitdiff.DiffLine{lineSection}, section.Lines...)
-		} else if direction == "down" {
+		case "down":
 			section.Lines = append(section.Lines, lineSection)
 		}
 	}