Fix bootstrapping presentation compiler

Author: noti0na1

project/Build.scala

@@ -1297,6 +1297,10 @@ object Build {
     .asScala3PresentationCompiler(NonBootstrapped)
   lazy val `scala3-presentation-compiler-bootstrapped` = project.in(file("presentation-compiler"))
     .asScala3PresentationCompiler(Bootstrapped)
+    .settings(
+      // Add `-Yno-flexible-types` flag for bootstrap, see comments for `bootstrappedDottyCompilerSettings`
+      Compile / scalacOptions +=  "-Yno-flexible-types"
+    )
 
   def scala3PresentationCompiler(implicit mode: Mode): Project = mode match {
     case NonBootstrapped => `scala3-presentation-compiler`