Skip DeathReaper tests when `pydiscourse` is not importable (#443)

Depending whether Poetry virtualenv contains `pydiscourse`,
it will skip or not `tests.unit.wot.exclusions`

pydiscourse is installed when specifying `poetry install --extras deathreaper`

https://docs.pytest.org/en/7.1.x/how-to/skipping.html#skipping-on-a-missing-import-dependency

tests/unit/wot/test_exclusions.py

@@ -15,6 +15,11 @@
 
 import pytest
 
+pytest.importorskip(
+    "pydiscourse",
+    reason="pydiscourse can't be imported, skipping deathreaper tests",
+)
+
 from silkaj.wot import exclusions