Fix warning headers

docs/reference/search/search-your-data/search-with-synonyms.asciidoc

@@ -75,16 +75,15 @@ A large number of inline synonyms increases cluster size unnecessarily and can l
 
 Once your synonyms sets are created, you can start configuring your token filters and analyzers to use them.
 
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 [WARNING]
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+=====
 Synonyms sets must exist before they can be added to indices.
 If an index is created referencing a nonexistent synonyms set, the index will remain in a partially created and inoperable state.
 The only way to recover from this scenario is to ensure the synonyms set exists then either delete and re-create the index, or close and re-open the index.
-======
+=====
 
 [WARNING]
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+=====
 Invalid synonym rules can cause errors when applying analyzer changes.
 For reloadable analyzers, this prevents reloading and applying changes.
 You must correct errors in the synonym rules and reload the analyzer.
@@ -94,7 +93,7 @@ An index with invalid synonym rules cannot be reopened, making it inoperable whe
 * A node containing the index starts
 * The index is opened from a closed state
 * A node restart occurs (which reopens the node assigned shards)
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+=====
 
 {es} uses synonyms as part of the <<analysis-overview,analysis process>>.
 You can use two types of <<analysis-tokenfilters,token filter>> to include synonyms: