patch 8.2.4020: debugger test fails

Problem:    Debugger test fails.
Solution:   Fix import statement.

src/testdir/test_debugger.vim

@@ -891,7 +891,7 @@ func Test_Backtrace_DefFunction()
   CheckCWD
   let file1 =<< trim END
     vim9script
-    import File2Function from './Xtest2.vim'
+    import './Xtest2.vim' as imp
 
     def SourceAnotherFile()
       source Xtest2.vim
@@ -899,7 +899,7 @@ func Test_Backtrace_DefFunction()
 
     def CallAFunction()
       SourceAnotherFile()
-      File2Function()
+      imp.File2Function()
     enddef
 
     def g:GlobalFunction()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4020,
 /**/
     4019,
 /**/