patch 8.2.3086: Vim9: breakpoint on "for" does not work

Problem:    Vim9: breakpoint on "for" does not work.
Solution:   Use the right line number in ISN_DEBUG. (closes #8486)
diff --git a/src/testdir/test_debugger.vim b/src/testdir/test_debugger.vim
index dbf2000..bb3a246 100644
--- a/src/testdir/test_debugger.vim
+++ b/src/testdir/test_debugger.vim
@@ -1017,6 +1017,13 @@
       # comment
       echo "second"
     enddef
+    def g:FuncForLoop()
+      eval 1
+      for i in [11, 22, 33]
+        eval i
+      endfor
+      echo "done"
+    enddef
   END
   call writefile(file, 'Xtest.vim')
 
@@ -1062,6 +1069,15 @@
   call RunDbgCmd(buf, ':call FuncComment()', ['function FuncComment', 'line 2: echo "first"  .. "one"'])
   call RunDbgCmd(buf, ':breakadd func 3 FuncComment')
   call RunDbgCmd(buf, 'cont', ['function FuncComment', 'line 5: echo "second"'])
+  call RunDbgCmd(buf, 'cont')
+
+  call RunDbgCmd(buf, ':breakadd func 2 FuncForLoop')
+  call RunDbgCmd(buf, ':call FuncForLoop()', ['function FuncForLoop', 'line 2: for i in [11, 22, 33]'])
+  call RunDbgCmd(buf, 'echo i', ['11'])
+  call RunDbgCmd(buf, 'next', ['function FuncForLoop', 'line 3: eval i'])
+  call RunDbgCmd(buf, 'next', ['function FuncForLoop', 'line 4: endfor'])
+  call RunDbgCmd(buf, 'next', ['function FuncForLoop', 'line 2: for i in [11, 22, 33]'])
+  call RunDbgCmd(buf, 'echo i', ['22'])
 
   call RunDbgCmd(buf, 'cont')
   call StopVimInTerminal(buf)