patch 8.2.1606: Vim9: cannot use "true" with has()

Problem:    Vim9: cannot use "true" with has().
Solution:   Use tv_get_bool(). (closes #6876)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index aefb1bf..9e384da 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -4763,7 +4763,7 @@
 	}
     }
 
-    if (argvars[1].v_type != VAR_UNKNOWN && tv_get_number(&argvars[1]) != 0)
+    if (argvars[1].v_type != VAR_UNKNOWN && tv_get_bool(&argvars[1]))
 	// return whether feature could ever be enabled
 	rettv->vval.v_number = x;
     else