patch 8.2.3419: a failing debug expression may make Vim unusable

Problem:    A failing debug expression may make Vim unusable.
Solution:   Suppress error messages. (closes #8848)
diff --git a/src/testdir/test_debugger.vim b/src/testdir/test_debugger.vim
index 71fdedc..957f5ac 100644
--- a/src/testdir/test_debugger.vim
+++ b/src/testdir/test_debugger.vim
@@ -271,9 +271,7 @@
   call RunDbgCmd(buf, 'breakd func a()', ['E475: Invalid argument: func a()'])
   call RunDbgCmd(buf, 'breakd func a', ['E161: Breakpoint not found: func a'])
   call RunDbgCmd(buf, 'breakd expr', ['E475: Invalid argument: expr'])
-  call RunDbgCmd(buf, 'breakd expr x', [
-	      \ 'E121: Undefined variable: x',
-	      \ 'E161: Breakpoint not found: expr x'])
+  call RunDbgCmd(buf, 'breakd expr x', ['E161: Breakpoint not found: expr x'])
 
   " finish the current function
   call RunDbgCmd(buf, 'finish', [