Activate include for Beats highlights (elastic#1311) (elastic#1316)

Author: dedemorton

docs/en/install-upgrade/highlights.asciidoc

@@ -33,7 +33,7 @@ coming::[7.9.0]
 
 This list summarizes the most important enhancements in {beats} {minor-version}.
 
-//include::{beats-repo-dir}/release-notes/whats-new.asciidoc[tag=notable-highlights]
+include::{beats-repo-dir}/release-notes/whats-new.asciidoc[tag=notable-highlights]
 
 [[elasticsearch-highlights]]
 === {es} highlights