Clear env before running env resolver tests

This updates the env credential resolver tests to clear the targeted
variables before any tests are run so that if they happen to be set
already they don't affect the tests.

Author: JordonPhillips

packages/smithy-aws-core/tests/unit/identity/test_environment_credentials_resolver.py

@@ -6,6 +6,14 @@
 from smithy_core.exceptions import SmithyIdentityError
 
 
+@pytest.fixture(autouse=True)
+def clear_environment(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("AWS_ACCOUNT_ID", raising=False)
+    monkeypatch.delenv("AWS_SECRET_ACCESS_KEY", raising=False)
+    monkeypatch.delenv("AWS_ACCESS_KEY_ID", raising=False)
+    monkeypatch.delenv("AWS_SESSION_TOKEN", raising=False)
+
+
 async def test_no_values_set():
     with pytest.raises(SmithyIdentityError):
         await EnvironmentCredentialsResolver().get_identity(properties={})