Update scala3-library to 3.6.4 (#184)

Co-authored-by: scala-center-steward[bot] <111975575+scala-center-steward[bot]@users.noreply.github.com>

Author: scala-center-steward[bot]

bin/generate-proposal-listing.scala

@@ -1,6 +1,6 @@
 #!/usr/local/bin/env -S scala-cli shebang
 
-//> using scala 3.6.3
+//> using scala 3.6.4
 //> using dep com.vladsch.flexmark:flexmark-all:0.64.8
 
 import java.io.PrintWriter