Don't install Tensorflow in the tests task

It forces the installation of numpy 1.19.5, which is incompatible with the latest version of shap.

.taskcluster.yml

@@ -97,7 +97,6 @@ tasks:
               cp infra/hgrc /etc/mercurial/hgrc.d/bugbug.rc &&
               pip install --disable-pip-version-check --no-cache-dir --progress-bar off -r requirements.txt &&
               pip install --disable-pip-version-check --no-cache-dir --progress-bar off -r extra-nlp-requirements.txt &&
-              pip install --disable-pip-version-check --no-cache-dir --progress-bar off -r extra-nn-requirements.txt &&
               pip install --disable-pip-version-check --no-cache-dir --progress-bar off -r infra/spawn_pipeline_requirements.txt &&
               pip install --disable-pip-version-check --no-cache-dir --progress-bar off -r test-requirements.txt &&
               hg clone -r f82da50255562126ccc794bcba23cd59661fadd1 https://hg.mozilla.org/hgcustom/version-control-tools /version-control-tools/ &&

tests/test_models.py

@@ -3,6 +3,8 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.
 
+import importlib
+
 from bugbug import model
 from bugbug.models import MODELS, get_model_class
 
@@ -13,6 +15,9 @@ def test_import_all_models():
     """
 
     for model_name in MODELS:
+        if model_name == "component_nn" and not importlib.util.find_spec("tensorflow"):
+            continue
+
         print("Try loading model", model_name)
         get_model_class(model_name)