chore: set key cache directory from the environment for make pytest command

frontends/concrete-python/Makefile

@@ -29,7 +29,8 @@ pytest:
 	pytest tests -svv -n auto \
 		--cov=concrete \
 		--cov-fail-under=100 \
-		--cov-report=term-missing:skip-covered
+		--cov-report=term-missing:skip-covered \
+		--key-cache "${KEY_CACHE_DIRECTORY}"
 
 # ==========
 # Formatting

frontends/concrete-python/tests/conftest.py

@@ -50,7 +50,7 @@ def pytest_sessionstart(session):
     # pylint: enable=global-statement
 
     key_cache_location = session.config.getoption("--key-cache", default=None)
-    if key_cache_location is not None:
+    if key_cache_location is not None and key_cache_location != "":
         if key_cache_location.lower() == "disable":
             key_cache_location = None
         else: