change(ci): do not trigger ci build if just docs changed

Source: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#example-excluding-paths

.github/workflows/main.yml

@@ -5,8 +5,12 @@ name: CI
 on:
   push:
     branches: [ main ]
+    paths-ignore:
+      - 'docs/**'
   pull_request:
     branches: [ main ]
+    paths-ignore:
+      - 'docs/**'
 
 env:
   DESECSTACK_DOMAIN: your.hostname.example.com