[release/3.6] Update versions.txt to 1.21.10 (#4667)

#4626

Author: Glavo

HMCLCore/src/main/resources/assets/game/versions.txt

@@ -846,4 +846,6 @@
 1.21.9-pre3
 1.21.9-pre4
 1.21.9-rc1
-1.21.9
+1.21.9
+1.21.10-rc1
+1.21.10