Only run docs workflow on main branch (#2105) (#2110)

Backport #2105

.woodpecker/docs.yml

@@ -1,8 +1,6 @@
 when:
-  - event: pull_request
-  - event: push
-    branch: [ main, release/* ]
-
+  event: [pull_request, push, cron]
+  branch: ${CI_REPO_DEFAULT_BRANCH}
 
 variables:
   - &golang_image 'golang:1.20.2'

.woodpecker/securityscan.yml

@@ -20,6 +20,9 @@ steps:
     settings:
       skip-dirs: node_modules/,plugins/woodpecker-plugins/node_modules/
       dir:  docs/
+    when:
+      event: [pull_request, push, cron]
+      branch: ${CI_REPO_DEFAULT_BRANCH}
 
   check web:
     group: check