Fix incorrect logout base (#3611)

Fixes #3608.

src/node/routes/logout.ts

@@ -8,7 +8,7 @@ router.get("/", async (req, res) => {
   // Must use the *identical* properties used to set the cookie.
   res.clearCookie(Cookie.Key, {
     domain: getCookieDomain(req.headers.host || "", req.args["proxy-domain"]),
-    path: req.body.base || "/",
+    path: req.query.base || "/",
     sameSite: "lax",
   })