patch 9.0.1723: Fix regression in {func} argument of reduce()

Problem: Fix regression in {func} argument of reduce()
Solution: pass function name as string again

Before patch 9.0.0548, passing a string as {func} argument of reduce()
is treated as a function name, but after patch 9.0.0548 it is treated as
an expression instead, which is useless as reduce() doesn't set any v:
variables. This PR restores the behavior of {func} before that patch.

Also correct an emsg() call, as e_string_list_or_blob_required doesn't
contain format specifiers.

closes: #12824

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/version.c b/src/version.c
index 1809d0d..de1d6e0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1723,
+/**/
     1722,
 /**/
     1721,