Add Scala 2.13.11 and 2.12.18 to plugin cross versions (backport #3327) (#3328)

* Add Scala 2.13.11 and 2.12.18 to plugin cross versions (#3327)

This enables Chisel users to use these newer Scala versions.

(cherry picked from commit b22c3ba2

)

# Conflicts:
#	build.sbt

* Resolve backport conflicts

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Co-authored-by: Jack Koenig <koenig@sifive.com>