dev-utils: fix busy refresh loop

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/great-needles-lay.md

@@ -0,0 +1,5 @@
+---
+'@backstage/dev-utils': patch
+---
+
+Fixed busy refresh loop that happened when registering a page at `/`.

packages/dev-utils/src/devApp/render.tsx

@@ -227,7 +227,11 @@ class DevAppBuilder {
 
     const DevApp = hot(hotModule)(this.build());
 
-    if (window.location.pathname === '/' && this.defaultPage) {
+    if (
+      window.location.pathname === '/' &&
+      this.defaultPage &&
+      this.defaultPage !== '/'
+    ) {
       window.location.pathname = this.defaultPage;
     }