Run markdownlint on drone, fix lint issue (#25040)

It currently does not run on 1.19 branch, resulting in lint error having
landed in https://github.com/go-gitea/gitea/pull/25016.

.drone.yml

@@ -963,6 +963,12 @@ trigger:
       - docs/**
 
 steps:
+  - name: lint-docs
+    image: node:18
+    commands:
+      - make deps-frontend
+      - make lint-frontend
+
   - name: build-docs
     image: golang:1.20
     commands:

docs/content/doc/packages/cran.zh-cn.md

@@ -90,4 +90,4 @@ install.packages("{package_name}")
 
 ```shell
 install.packages("testpackage")
-```
+```