patch 8.2.4181: Vim9: cannot use an import in 'diffexpr'

Problem:    Vim9: cannot use an import in 'diffexpr'.
Solution:   Set the script context when evaluating 'diffexpr'.  Do not require
            'diffexpr' to return a bool, it was ignored anyway.
diff --git a/src/version.c b/src/version.c
index 88d32ff..cc5c101 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4181,
+/**/
     4180,
 /**/
     4179,