DOCS-250 Update antora.yml to 5.26.20

Author: NataliaIvakina

antora.yml

@@ -9,7 +9,7 @@ nav:
 asciidoc:
   attributes:
     neo4j-version: '5.26'
-    neo4j-version-exact: '5.26.19'
+    neo4j-version-exact: '5.26.20'
     neo4j-buildnumber: '5.26'
     java-driver-version: '5.28.10'
     neo4j-documentation-branch: 'dev'