do not check links on docs.github.com (#4578)

# Objective

- related to #4575, but not a complete fix
- links to GitHub.com can't be checked from inside a GitHub Actions as GitHub is protecting itself from being flooded by an action execution
- it seems they added that protection to GitHub doc site

## Solution

- Ignore links to docs.github.com

.github/linters/markdown-link-check.json

@@ -3,6 +3,9 @@
     {
       "pattern": "^https?://github\\.com/"
     },
+    {
+      "pattern": "^https?://docs\\.github\\.com/"
+    },
     {
       "pattern": "^https?://reddit\\.com/"
     }