patch 8.2.1516: Vim9: error for :exe has wrong line number

Problem:    Vim9: error for :exe has wrong line number.
Solution:   Set line number before calling do_cmdline_cmd(). (closes #6774)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index a49f3d7..53a748e 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -1062,7 +1062,10 @@
 		    if (ga.ga_data != NULL)
 		    {
 			if (iptr->isn_type == ISN_EXECUTE)
+			{
+			    SOURCING_LNUM = iptr->isn_lnum;
 			    do_cmdline_cmd((char_u *)ga.ga_data);
+			}
 			else
 			{
 			    msg_sb_eol();