Remove locale dependent FileSystemException check

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.

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.

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)