[CI/Build] Trigger processor tests on registry update (#35824)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

.buildkite/test_areas/models_multimodal.yaml

@@ -20,6 +20,7 @@ steps:
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
+  - tests/models/registry.py
   device: cpu
   commands:
     - pip install git+https://github.com/TIGER-AI-Lab/Mantis.git
@@ -30,6 +31,7 @@ steps:
   source_file_dependencies:
   - vllm/
   - tests/models/multimodal
+  - tests/models/registry.py
   commands:
     - pip install git+https://github.com/TIGER-AI-Lab/Mantis.git
     - pytest -v -s models/multimodal/processing/test_tensor_schema.py
@@ -70,12 +72,3 @@ steps:
   commands:
     - pip install git+https://github.com/TIGER-AI-Lab/Mantis.git
     - pytest -v -s models/multimodal/generation/test_common.py -m 'split(group=1) and not core_model'
-
-# This test is used only in PR development phase to test individual models and should never run on main
-- label: Custom Models
-  optional: true
-  commands:
-    - echo 'Testing custom models...'
-    # PR authors can temporarily add commands below to test individual models
-    # e.g. pytest -v -s models/encoder_decoder/vision_language/test_mllama.py
-    # *To avoid merge conflicts, remember to REMOVE (not just comment out) them before merging the PR*