Fix incorrect parser used in nightly scaladoc

Previously a sourceDirectory sbt task would resolve to
"library/src/main" which usually would be correct, but in the case of
the scala 3 library, we have the sources directly under `library/src`
This lead to the fact that the incorrectly set `-comment-syntax` option
could never match against the prefix for markdown, and would use the
wiki syntax for all scala3-library sources.

Author: jchyb

project/Build.scala

@@ -2207,8 +2207,7 @@ object ScaladocConfigs {
     val stdLibRoot = projectRoot.relativize(managedSources.toPath.normalize())
     val docRootFile = stdLibRoot.resolve("rootdoc.txt")
 
-    val dottyManagesSources =
-      (`scala3-library-bootstrapped`/Compile/sourceDirectory).value
+    val dottyManagesSources = (`scala3-library-bootstrapped`/Compile/baseDirectory).value
 
     val tastyCoreSources = projectRoot.relativize((`tasty-core-bootstrapped`/Compile/scalaSource).value.toPath().normalize())