revert to Scala 3.3

> Scala 3.4.0 code can depend on dependencies compiled with Scala 3.3.x, but not the other way around. That means that if you are a library author, you should consider staying on the LTS line.

scala/scala-lang#1598

Author: xuwei-k

build.sbt

@@ -6,7 +6,7 @@ lazy val root = (project in file(".")).settings(
   name := "scalamd",
   version := "1.7.4-SNAPSHOT",
   scalaVersion := Scala212,
-  crossScalaVersions := Seq(Scala212, "2.11.12", "2.10.7", "2.13.13", "3.4.0"),
+  crossScalaVersions := Seq(Scala212, "2.11.12", "2.10.7", "2.13.13", "3.3.2"),
   transitiveClassifiers in Global := Seq(Artifact.SourceClassifier),
   scalacOptions ++= Seq("-unchecked", "-deprecation", "-feature"),
   scalatestVersion := "3.2.18",