Update default Guava dependency for Jackson 2.15 from Guava 21.0 to 23.6.1-jre

[cowtowncoder]

Although Guava module can work with older versions, there is some value in increasing the default transitive dependency version.
Since we have kept it at 21.x since 2.12 let's upgrade to last 23.x (... from 2018) for Jackson 2.15.