patch 9.0.0687: "export def" does not work in a nested block

Problem:    "export def" does not work in a nested block.
Solution:   Do not handle "export" with a separate function but in the same
            command stack. (closes #11304)
diff --git a/src/testdir/test_vim9_import.vim b/src/testdir/test_vim9_import.vim
index e844d4a..d509007 100644
--- a/src/testdir/test_vim9_import.vim
+++ b/src/testdir/test_vim9_import.vim
@@ -452,6 +452,21 @@
   delete('Xlib.vim')
 enddef
 
+def Test_export_closure()
+  # tests that the closure in block can be compiled, not the import part
+  var lines =<< trim END
+      vim9script
+      {
+        var foo = 42
+        export def Bar(): number
+          return foo
+        enddef
+      }
+      assert_equal(42, Bar())
+  END
+  v9.CheckScriptSuccess(lines)
+enddef
+
 def Test_import_duplicate_function()
   # Function Hover() exists in both scripts, partial should refer to the right
   # one.
@@ -1513,7 +1528,7 @@
   v9.CheckScriptFailure(['vim9script', 'export echo 134'], 'E1043:')
   v9.CheckScriptFailure(['vim9script', 'export function /a1b2c3'], 'E1044:')
 
-  assert_fails('export something', 'E1043:')
+  assert_fails('export echo 1', 'E1043:')
 enddef
 
 func Test_import_fails_without_script()