Add more precompiled bridge versions

Author: lefou

build.mill

@@ -97,6 +97,8 @@ val bridgeScalaVersions = Seq(
   "2.12.17",
   "2.12.18",
   "2.12.19",
+  "2.12.20",
+  "2.12.21",
   /*"2.13.0", "2.13.1", "2.13.2",*/
   "2.13.3",
   "2.13.4",