tests: add a project group to our test manifest

Exercise that this round-trips properly through a west manifest
--freeze.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

tests/conftest.py

@@ -42,6 +42,8 @@ manifest:
     - name: Kconfiglib
       revision: zephyr
       path: subdir/Kconfiglib
+      groups:
+        - Kconfiglib-group
     - name: tagged_repo
       revision: v1.0
     - name: net-tools

tests/test_project.py

@@ -242,6 +242,8 @@ def test_manifest_freeze(west_update_tmpdir):
                     '^    url: .*$',
                     '^    revision: [a-f0-9]{40}$',
                     '^    path: subdir/Kconfiglib$',
+                    '^    groups:$',
+                    '^    - Kconfiglib-group$',
                     '^  - name: tagged_repo$',
                     '^    url: .*$',
                     '^    revision: [a-f0-9]{40}$',