patch 8.2.1543: Vim9: test with invalid SID is skipped in the GUI

Problem:    Vim9: test with invalid SID is skipped in the GUI.
Solution:   Read the CTRL-C that feedkeys() put in typeahead.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 6d520a3..8ebcc28 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -2364,6 +2364,8 @@
     assert_equal(100, x)
   endtry
   assert_true(caught, 'should have caught an exception')
+  # consume the CTRL-C
+  getchar(0)
 enddef
 
 def Test_automatic_line_continuation()
@@ -3177,7 +3179,7 @@
     " caught
   endtry
 
-  call delete('Xvim9script.vium')
+  call delete('Xvim9script.vim')
 endfunc
 
 def Test_vim9_copen()
@@ -3261,10 +3263,8 @@
 enddef
 
 def Test_invalid_sid()
-  # TODO: why does this not work in the GUI?
-  CheckNotGui
-
   assert_fails('func <SNR>1234_func', 'E123:')
+
   if RunVim([], ['wq Xdidit'], '+"func <SNR>1_func"')
     call assert_equal([], readfile('Xdidit'))
   endif
diff --git a/src/version.c b/src/version.c
index 1a66eb6..8eaf484 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1543,
+/**/
     1542,
 /**/
     1541,