patch 8.2.2757: Vim9: blob tests for legacy and Vim9 script are separate

Problem:    Vim9: blob tests for legacy and Vim9 script are separate.
Solution:   Add CheckLegacyAndVim9Success().  Make blob index assign work.
diff --git a/src/proto/blob.pro b/src/proto/blob.pro
index 6be7f0b..7da269c 100644
--- a/src/proto/blob.pro
+++ b/src/proto/blob.pro
@@ -14,5 +14,6 @@
 char_u *blob2string(blob_T *blob, char_u **tofree, char_u *numbuf);
 blob_T *string2blob(char_u *str);
 int blob_slice_or_index(blob_T *blob, int is_range, varnumber_T n1, varnumber_T n2, int exclusive, typval_T *rettv);
+int blob_set_range(blob_T *dest, long n1, long n2, typval_T *src);
 void blob_remove(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */