Fixed errcheck issues in server/channels/app/plugin_install.go (#29062)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/i18n/en.json

@@ -6154,6 +6154,10 @@
     "id": "app.plugin.restart.app_error",
     "translation": "Unable to restart plugin on upgrade."
   },
+  {
+    "id": "app.plugin.seek.app_error",
+    "translation": "Unable to reset the read position to the start of the plugin bundle."
+  },
   {
     "id": "app.plugin.signature_decode.app_error",
     "translation": "Unable to decode base64 signature."