chore: update Minecraft versions (#462)

Co-authored-by: moddermore-bot[bot] <207009453+moddermore-bot[bot]@users.noreply.github.com>

Author: moddermore-bot[bot]

src/lib/minecraftVersions.json

@@ -522,6 +522,7 @@
     "13w16a",
     "3D Shareware v1.34",
     "1.RV-Pre1",
+    "1.21.6-pre3",
     "1.21.6-pre2",
     "1.21.6-pre1",
     "1.21.5-rc2",