Use a more portable way to download an old compiler for tests

Author: prolativ

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -1426,9 +1426,9 @@ object ParallelTesting {
         dir
       else
         import scala.sys.process._
-        val zipPath = cache.resolve(s"scala3-$version.zip")
-        val compilerDownloadUrl = s"https://github.com/lampepfl/dotty/releases/download/$version/scala3-$version.zip"
-        (URL(compilerDownloadUrl) #>> zipPath.toFile #&& s"unzip $zipPath -d $cache").!!
+        val zipPath = cache.resolve(s"scala3-$version.tar.gz")
+        val compilerDownloadUrl = s"https://github.com/lampepfl/dotty/releases/download/$version/scala3-$version.tar.gz"
+        (URL(compilerDownloadUrl) #>> zipPath.toFile #&& s"tar -xf $zipPath -C $cache").!!
         dir
     }