Use os.getenv() instead of os.environ

If ECDSAP256SHA256_SUPPORTED or ECDSAP384SHA384_SUPPORTED variables were
not present in the environment, os.environ would raise KeyError that is
not being handled in the decorator. Use os.getenv() instead.

bin/tests/system/ecdsa/tests_ecdsa.py

@@ -38,15 +38,15 @@ def check_server_soa(resolver):
 
 
 @pytest.mark.skipif(
-    not os.environ["ECDSAP256SHA256_SUPPORTED"],
+    not os.getenv("ECDSAP256SHA256_SUPPORTED"),
     reason="algorithm ECDSA256 not supported",
 )
 def test_ecdsa256():
     check_server_soa("10.53.0.2")
 
 
 @pytest.mark.skipif(
-    not os.environ["ECDSAP384SHA384_SUPPORTED"],
+    not os.getenv("ECDSAP384SHA384_SUPPORTED"),
     reason="algorithm ECDSA384 not supported",
 )
 def test_ecdsa384():