proper os_name "linux" instead of "linux_arm" (amending a33a6e541cbb);

--- a/src/Pure/System/isabelle_platform.scala	Wed Jan 31 21:25:09 2024 +0100
+++ b/src/Pure/System/isabelle_platform.scala	Wed Jan 31 21:50:50 2024 +0100
@@ -59,7 +59,7 @@
   def arch_64: String = if (is_arm) "arm64" else "x86_64"
   def arch_64_32: String = if (is_arm) "arm64_32" else "x86_64_32"
 
-  def os_name: String = if (is_macos) "darwin" else ISABELLE_PLATFORM_FAMILY
+  def os_name: String = if (is_macos) "darwin" else if (is_windows) "windows" else "linux"
 
   override def toString: String = ISABELLE_PLATFORM_FAMILY
 }