improve(tests): add scenario to test against plugins downloader in monothread and forced

tests/fixtures/scenarios/good_scenario_plugins_downloader_force.qdt.yml

@@ -0,0 +1,41 @@
+# yaml-language-server: $schema=https://raw.githubusercontent.com/Guts/qgis-deployment-cli/main/docs/schemas/scenario/schema.json
+
+# This is a sample of a YAML file for the QGIS Deployment Toolbelt scenario.
+# For now, it's more a roadmap than a real description of what it's implemented.
+
+metadata:
+  title: "Test scenario of QDT with monothreaded and forced plugins downloader"
+  id: test-scenario-good-plugins-downloader-forced-monothreaded
+  description: >-
+    This is an example a scenario YAML file for the QGIS Deployment Toolbelt to
+    try plugins downloader capabilities.
+
+settings:
+  DEBUG: false
+  LOCAL_WORK_DIR: ~/.cache/qgis-deployment-toolbelt/tests/
+  SCENARIO_VALIDATION: true
+
+steps:
+  - name: Download profiles from remote git repository
+    uses: qprofiles-downloader
+    with:
+      source: https://github.com/Guts/qgis-deployment-cli.git
+      protocol: git_remote
+      branch: main
+
+  - name: Synchronize downloaded profiles with installed ones
+    uses: qprofiles-synchronizer
+    with:
+      sync_mode: only_new_version
+
+  - name: Download plugins
+    uses: qplugins-downloader
+    with:
+      force: true
+      threads: 1
+
+  - name: Synchronize plugins
+    uses: qplugins-synchronizer
+    with:
+      action: create_or_restore
+      profile_ref: installed