patch 9.0.1897: Vim9: confusing error with .= in compiled functions

Problem:  Vim9: confusing error with .= in compiled functions
Solution: Check in error condition, if .= was attempted and in that case
          give a different error message.

closes: #12972
closes: #13066

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 937f8b8..aaa50da 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1897,
+/**/
     1896,
 /**/
     1895,