patch 8.2.0578: heredoc for interfaces does not support "trim"

Problem:    Heredoc for interfaces does not support "trim".
Solution:   Update the script heredoc support to be same as the :let command.
            (Yegappan Lakshmanan, closes #5916)
diff --git a/src/version.c b/src/version.c
index 15a9393..2f64d5a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    578,
+/**/
     577,
 /**/
     576,