Exclude mail links in links.yml workflow

Exclude mail links from the link checking workflow.

Author: djpbarry

.github/workflows/links.yml

@@ -25,6 +25,7 @@ jobs:
             --verbose
             --no-progress
             --accept 200,206,429
+            --exclude-mail
             --max-concurrency 4
             './**/*.md'
             './**/*.html'