Filtering of requests only shows requests from expanded folders

**Describe the bug**
Filtering requests only filters requests from folders that are expanded.

**To Reproduce**
Steps to reproduce the behavior:
1. Open a collection/document
2. Type something in the filter text box below the environment selection

**Expected behavior**
All requests matching the text pattern entered in the filter text box should show in the request selection panel.

**Desktop (please complete the following information):**
- Debian 11 (Bullseye)
- Flatpak
- 21.4.1

Reproduce the filtering behavior in a collection or document with collapsed folders, following the steps in the issue. Inspect the request selection panel and its filter implementation, then verify that matching requests from collapsed folders appear while existing filtering behavior remains intact.

Written by the indexing model from the issue text.