[DOCS] Escape depcreated[] note for Asciidoctor migration (#41608)

docs/reference/commands/certgen.asciidoc

@@ -3,7 +3,7 @@
 [[certgen]]
 == elasticsearch-certgen
 
-deprecated[6.1,Replaced by <<certutil,`elasticsearch-certutil`>>.]
+deprecated[6.1,"Replaced by <<certutil,`elasticsearch-certutil`>>."]
 
 The `elasticsearch-certgen` command simplifies the creation of certificate
 authorities (CA), certificate signing requests (CSR), and signed certificates