patch 8.2.2951: Vim9: cannot use heredoc for :python, :lua, etc.

Problem:    Vim9: cannot use heredoc in :def function for :python, :lua, etc.
Solution:   Concatenate the heredoc lines and pass them in the ISN_EXEC_SPLIT
            instruction.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2951,
 /**/
     2950,
 /**/