fix(i18n): name the Russian download throughput label as a noun (#6890)

pages.index.download labels the download-speed figure on the dashboard next to
"Загрузка" (upload). The imperative "Скачать" read as a button; the noun
"Скачивание" matches what the label shows. CI does not run on translation-only
changes; the file still parses as JSON.

internal/web/translation/ru-RU.json

@@ -210,7 +210,7 @@
       "toggleIpVisibility": "Скрыть или показать IP-адреса сервера",
       "overallSpeed": "Общая скорость передачи трафика",
       "upload": "Загрузка",
-      "download": "Скачать",
+      "download": "Скачивание",
       "sent": "Отправлено",
       "received": "Получено",
       "xraySwitchVersionDialog": "Переключить версию Xray",