patch 8.2.2692: Vim9: locked script variable can be changed

Problem:    Vim9: locked script variable can be changed.
Solution:   Check for locked value. (closes #8031)

src/testdir/test_vim9_assign.vim

@@ -1346,6 +1346,17 @@ def Test_var_declaration_fails()
   CheckScriptFailure(lines, 'E741:')
   unlet g:constvar
 
+  lines =<< trim END
+    vim9script
+    var name = 'one'
+    lockvar name
+    def SetLocked()
+      name = 'two'
+    enddef
+    SetLocked()
+  END
+  CheckScriptFailure(lines, 'E741: Value is locked: name')
+
   lines =<< trim END
     vim9script
     def SetGlobalConst()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2692,
 /**/
     2691,
 /**/

src/vim9execute.c

@@ -1958,6 +1958,13 @@ call_def_function(
 		    if (sv == NULL)
 			goto failed;
 		    --ectx.ec_stack.ga_len;
+
+		    // "const" and "final" are checked at compile time, locking
+		    // the value needs to be checked here.
+		    SOURCING_LNUM = iptr->isn_lnum;
+		    if (value_check_lock(sv->sv_tv->v_lock, sv->sv_name, FALSE))
+			goto on_error;
+
 		    clear_tv(sv->sv_tv);
 		    *sv->sv_tv = *STACK_TV_BOT(0);
 		}