Update dependency net.fabricmc:yarn to v1.21-pre2+build.2

Author: renovate[bot]

gradle.properties

@@ -3,7 +3,7 @@ org.gradle.jvmargs=-Xmx4G
 # Fabric
 # check these on https://fabricmc.net/develop/
 minecraft_version=1.20.4
-yarn_mappings=1.20.6+build.1
+yarn_mappings=1.21-pre2+build.2
 loader_version=0.15.11
 fabric_version=0.97.8+1.20.6