Remove locale dependent FileSystemException check

Fin SourceFile, files that do not exist are expected and related exceptions
should be ignored. There are two relevant cases:

    scala> java.nio.file.Files.newInputStream(java.nio.file.FileSystems.getDefault().getPath("does-not-exist"))
    java.nio.file.NoSuchFileException: does-not-exist

    scala> java.nio.file.Files.newInputStream(java.nio.file.FileSystems.getDefault().getPath("regular-file-instead-of-directory/filename"))
    java.nio.file.FileSystemException: regular-file-instead-of-directory/filename: Not a directory

Ideally, other I/O errors would be propagated to the caller.

However, there is no reliable way to distinguish them based on the
exceptions alone. In particular, the message cannot be checked, because
it depends on the operating system and it is localized.

Revert the addition of the check and just accept this.

compiler/src/dotty/tools/dotc/util/SourceFile.scala

@@ -275,12 +275,11 @@ object SourceFile {
 
   def apply(file: AbstractFile | Null, codec: Codec): SourceFile =
     // Files.exists is slow on Java 8 (https://rules.sonarsource.com/java/tag/performance/RSPEC-3725),
-    // so cope with failure; also deal with path prefix "Not a directory".
+    // so cope with failure.
     val chars =
       try new String(file.toByteArray, codec.charSet).toCharArray
       catch
-        case _: NoSuchFileException => Array.empty[Char]
-        case fse: FileSystemException if fse.getMessage.endsWith("Not a directory") => Array.empty[Char]
+        case _: FileSystemException => Array.empty[Char]
 
     if isScript(file, chars) then
       ScriptSourceFile(file, chars)