patch 8.2.1342: Vim9: accidentally using "t" gives a confusing error

Problem:    Vim9: accidentally using "x" gives a confusing error.
Solution:   Disallow using ":t" in Vim9 script. (issue #6399)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index ad1693b..081d9e4 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -7276,6 +7276,9 @@
 {
     long	n;
 
+    if (not_in_vim9(eap) == FAIL)
+	return;
+
     n = get_address(eap, &eap->arg, eap->addr_type, FALSE, FALSE, FALSE, 1);
     if (eap->arg == NULL)	    // error detected
     {
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index c01b383..8950f31 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1628,18 +1628,21 @@
 enddef
 
 def Test_no_insert_xit()
-  call CheckDefExecFailure(['x = 1'], 'E1100:')
   call CheckDefExecFailure(['a = 1'], 'E1100:')
-  call CheckDefExecFailure(['i = 1'], 'E1100:')
   call CheckDefExecFailure(['c = 1'], 'E1100:')
+  call CheckDefExecFailure(['i = 1'], 'E1100:')
+  call CheckDefExecFailure(['t = 1'], 'E1100:')
+  call CheckDefExecFailure(['x = 1'], 'E1100:')
 
-  CheckScriptFailure(['vim9script', 'x = 1'], 'E1100:')
   CheckScriptFailure(['vim9script', 'a = 1'], 'E488:')
   CheckScriptFailure(['vim9script', 'a'], 'E1100:')
-  CheckScriptFailure(['vim9script', 'i = 1'], 'E488:')
-  CheckScriptFailure(['vim9script', 'i'], 'E1100:')
   CheckScriptFailure(['vim9script', 'c = 1'], 'E488:')
   CheckScriptFailure(['vim9script', 'c'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'i = 1'], 'E488:')
+  CheckScriptFailure(['vim9script', 'i'], 'E1100:')
+  CheckScriptFailure(['vim9script', 't'], 'E1100:')
+  CheckScriptFailure(['vim9script', 't = 1'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'x = 1'], 'E1100:')
 enddef
 
 def IfElse(what: number): string
diff --git a/src/version.c b/src/version.c
index 202ee2f..021487d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1342,
+/**/
     1341,
 /**/
     1340,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 97fa2e0..38c097c 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -7467,6 +7467,7 @@
 	    case CMD_append:
 	    case CMD_change:
 	    case CMD_insert:
+	    case CMD_t:
 	    case CMD_xit:
 		    not_in_vim9(&ea);
 		    goto erret;
diff --git a/src/vim9script.c b/src/vim9script.c
index 2e94b8e..e7bb433 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -67,9 +67,10 @@
     if (in_vim9script())
 	switch (eap->cmdidx)
 	{
-	    case CMD_insert:
 	    case CMD_append:
 	    case CMD_change:
+	    case CMD_insert:
+	    case CMD_t:
 	    case CMD_xit:
 		semsg(_("E1100: Missing :let: %s"), eap->cmd);
 		return FAIL;