patch 8.2.4643: Vim9: variable may be locked unintentionally

Problem:    Vim9: variable may be locked unintentionally.
Solution:   Clear "v_lock". (closes #10036)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index a95a488..c5dc30d 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -937,6 +937,7 @@
     tv = STACK_TV_BOT(-1);
     tv->v_type = VAR_NUMBER;
     tv->vval.v_number = 0;
+    tv->v_lock = 0;
 
     return OK;
 }