Add context dictionary support to lambda

** Why are these changes being introduced:

* At the moment, running the curl command from the project readme in a
terminal results in an argument error, rather than the stated response.

** Relevant ticket(s):

n/a

** How does this address that need:

* This adds a second dictionary as an argument to the lambda_handler
method in predict.py. The same change is made to the two tests which
actually call this fuction.

This now matches what the s3-bagit lambda is expecting, which I'm using
as a starting point for my work in this repo:

Handler:
https://github.com/MITLibraries/s3-bagit-validator/blob/main/lambdas/validator.py#L29

Test:
https://github.com/MITLibraries/s3-bagit-validator/blob/main/tests/test_lambda_handler.py#L20

** Document any side effects to this change:

I'm not sure whether this is going to bite me later or not - that will
need to wait until this gets deployed to AWS.

Author: matt-bernhardt

lambdas/predict.py

@@ -23,7 +23,7 @@
     logger.info("No Sentry DSN found, exceptions will not be sent to Sentry")
 
 
-def lambda_handler(event: dict) -> str:
+def lambda_handler(event: dict, _context: dict) -> str:
     if not os.getenv("WORKSPACE"):
         unset_workspace_error_message = "Required env variable WORKSPACE is not set"
         raise RuntimeError(unset_workspace_error_message)

tests/test_predict.py

@@ -22,9 +22,9 @@ def test_predict_doesnt_configure_sentry_if_dsn_not_present(caplog, monkeypatch)
 def test_lambda_handler_missing_workspace_env_raises_error(monkeypatch):
     monkeypatch.delenv("WORKSPACE", raising=False)
     with pytest.raises(RuntimeError) as error:
-        predict.lambda_handler({})
+        predict.lambda_handler({}, {})
     assert "Required env variable WORKSPACE is not set" in str(error)
 
 
 def test_predict():
-    assert predict.lambda_handler({}) == "You have successfully called this lambda!"
+    assert predict.lambda_handler({}, {}) == "You have successfully called this lambda!"