fix(proxy-rewrite): fix url normalization bypass

This commit fixes a bug where ctx.var.upstream_uri is
not set when use_real_request_uri_unsafe is enabled.

It seems that somewhere in the runtime chain (LuaJIT?)
a memory jump occurs and ctx.var.upstream_uri _does_ get set
even though it definitely **shouldn't**. Hence why this got unnoticed
in the CI tests of apache#7401.

Signed-off-by: İlteriş Yağıztegin Eroğlu <ilteris.eroglu@trendyol.com>

apisix/plugins/proxy-rewrite.lua

@@ -297,6 +297,8 @@ do
         else
             ctx.var.upstream_uri = upstream_uri
         end
+    else
+        ctx.var.upstream_uri = upstream_uri
     end
 
     if conf.headers then