ci: verify no {{ }} placeholders in man page examples

Author: sylvestre

.github/workflows/documentation.yml

@@ -129,3 +129,4 @@ jobs:
           cargo run --bin uudoc --all-features -- manpage cp > /tmp/cp.1
           grep -q "\.SH EXAMPLES" /tmp/cp.1
           grep -q "tldr-pages" /tmp/cp.1
+          ! grep -q "{{" /tmp/cp.1