patch 9.1.0459: Vim9: import autoload does not work with symlink

Problem:  Vim9: import autoload does not work with symlink
          (Olivier Dormond)
Solution: set sn_autoload_prefix in check_script_symlink
          (nwounkn)

fixes: #14775
closes: #14885

Signed-off-by: nwounkn <nwounkn@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_vim9_import.vim b/src/testdir/test_vim9_import.vim
index 3067ef6..fb309cb 100644
--- a/src/testdir/test_vim9_import.vim
+++ b/src/testdir/test_vim9_import.vim
@@ -3068,7 +3068,10 @@
     var lines =<< trim END
         vim9script
         import autoload 'bar.vim'
-        g:resultFunc = bar.Func()
+        def FooFunc(): string
+          return bar.Func()
+        enddef
+        g:resultFunc = FooFunc()
         g:resultValue = bar.value
     END
     writefile(lines, 'Xto/plugin/foo.vim')