vim-patch:8.2.0614: get ml_get error when deleting a line in 'completefunc' (#19244)

Problem:    Get ml_get error when deleting a line in 'completefunc'. (Yegappan
            Lakshmanan)
Solution:   Lock the text while evaluating 'completefunc'.
ff06f283e3

Fix a mistake in the porting of patch 8.1.0098.
Cherry-pick Test_run_excmd_with_text_locked() from patch 8.2.0270.
Cherry-pick test_gf.vim changes from patch 8.2.0369.
Cherry-pick message change from later patches.

src/nvim/ex_getln.c

@@ -2722,7 +2722,7 @@ char *get_text_locked_msg(void)
   if (cmdwin_type != 0) {
     return e_cmdwin;
   } else {
-    return e_secure;
+    return e_textlock;
   }
 }