patch 8.2.0760: Vim9: dict member errors not tested

Problem:    Vim9: dict member errors not tested.
Solution:   Delete unreachable error.  Add tests.
diff --git a/src/version.c b/src/version.c
index 1eb94bd..d447c4b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    760,
+/**/
     759,
 /**/
     758,