fix: use inline secrets provider for test_secrets

The previous flow used @Secrets(sources=["mf_secrets_test"]) which
requires a configured default secrets backend (e.g. AWS Secrets Manager).
Switch to the inline provider with explicit type and options dict so
the test works on all backends without external secrets infrastructure.

Author: Nissan Pow

test/ux/core/flows/basic/hellosecrets.py

@@ -5,18 +5,23 @@
 class HelloSecretsFlow(FlowSpec):
     @step
     def start(self):
-        from metaflow import metaflow_version
-
-        print(f"In start step and using metaflow: {metaflow_version.get_version()}")
         print("HelloSecretsFlow is starting.")
         self.next(self.hello)
 
-    @secrets(sources=["mf_secrets_test"])
+    @secrets(
+        sources=[
+            {
+                "type": "inline",
+                "id": "test-secret",
+                "options": {"env_vars": {"MY_SECRET_VALUE": "hellosecrets"}},
+            }
+        ]
+    )
     @step
     def hello(self):
         import os
 
-        self.secrets = os.environ["mf_secrets_test"]
+        self.secrets = os.environ["MY_SECRET_VALUE"]
         print("Hello secrets: %s" % self.secrets)
         self.next(self.end)