[DOCS] Escape commas in deprecated[] for Asciidoctor migration (#41598)

Author: jrodewig

docs/reference/mapping/params/boost.asciidoc

@@ -73,7 +73,7 @@ have a higher score than words that originated in the `content` field.
 This functionality comes at a cost: queries on the `_all` field are slower
 when field boosting is used.
 
-deprecated[5.0.0, index time boost is deprecated.  Instead, the field mapping boost is applied at query time. For indices created before 5.0.0 the boost will still be applied at index time.]
+deprecated[5.0.0, "index time boost is deprecated.  Instead, the field mapping boost is applied at query time. For indices created before 5.0.0 the boost will still be applied at index time."]
 [WARNING]
 .Why index time boosting is a bad idea
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