Update sbt to 1.6.1

Co-authored-by: foundweekends-bot[bot] <74864734+foundweekends-bot[bot]@users.noreply.github.com>
Co-authored-by: kenji yoshida <6b656e6a69@gmail.com>

Author: foundweekends-bot[bot]

project/build.properties

@@ -1 +1 @@
-sbt.version=1.2.8
+sbt.version=1.6.1