deps: update dependency com.google.code.gson:gson to v2.8.9

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.google.code.gson:gson	2.8.8 -> 2.8.9

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Release Notes

google/gson

v2.8.9

• Make OSGi bundle's dependency on sun.misc optional (#​1993).
• Deprecate Gson.excluder() exposing internal Excluder class (#​1986).
• Prevent Java deserialization of internal classes (#​1991).
• Improve number strategy implementation (#​1987).
• Fix LongSerializationPolicy null handling being inconsistent with Gson (#​1990).
• Support arbitrary Number implementation for Object and Number deserialization (#​1290).
• Bump proguard-maven-plugin from 2.4.0 to 2.5.1 (#​1980).
• Don't exclude static local classes (#​1969).
• Fix RuntimeTypeAdapterFactory depending on internal Streams class (#​1959).
• Improve Maven build (#​1964).
• Make dependency on java.sql optional (#​1707).

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