CompatHelper: bump compat for "DocStringExtensions" to "0.9" (#601)

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Author: github-actions[bot]

Project.toml

@@ -17,7 +17,7 @@ Serialization = "9e88b42a-f829-5b0c-bbe9-9e923198166b"
 Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"
 
 [compat]
-DocStringExtensions = "0.8"
+DocStringExtensions = "0.8, 0.9"
 MPIPreferences = "0.1.2"
 Requires = "~0.5, 1.0"
 julia = "1.6"