test(workbenches): introduce a new test for ImageStreams from trainer

The new 3 ImageStreams from trainer component were introduced in the
product, we should test them similarly we do for the workbenches
ImageStreams.

Signed-off-by: Jan Stourac <jstourac@redhat.com>

Author: jstourac

tests/workbenches/README.md

@@ -16,7 +16,7 @@ workbenches/
 
 ### Current Test Suites
 
-- **`test_imagestream_health.py`** - Validates that workbench ImageStreams are properly imported and resolved. Checks correct ImageStream counts, tag digest references (`@sha256:`), and `ImportSuccess` conditions for both notebook images (11 expected) and runtime images (7 expected)
+- **`test_imagestream_health.py`** - Validates that ImageStreams are properly imported and resolved. Uses compound label selectors (`opendatahub.io/notebook-image` or `opendatahub.io/runtime-image` combined with `platform.opendatahub.io/part-of`) to scope checks per component. Validates correct ImageStream counts, tag digest references (`@sha256:`), and `ImportSuccess` conditions for workbench notebook images (11 expected), workbench runtime images (7 expected), and trainer images (3 expected)
 - **`notebook-controller/test_spawning.py`** - Tests basic notebook creation via Notebook CR and validates pod creation. Also tests Auth proxy container resource customization via annotations
 - **`notebook-controller/test_custom_images.py`** - Validates custom workbench images contain required Python packages by spawning a workbench, installing any missing packages, and executing import verification
 

tests/workbenches/test_imagestream_health.py

@@ -186,6 +186,11 @@ def _validate_imagestreams_with_label(
             7,
             id="runtime_imagestreams",
         ),
+        pytest.param(
+            "opendatahub.io/notebook-image=true,platform.opendatahub.io/part-of=trainer",
+            3,
+            id="trainer_imagestreams",
+        ),
     ],
 )
 def test_workbench_imagestreams_health(