fix(spark): drop the stray argument passed to _backend_config in the advanced-options example

[Anai-Guo]

Problem

examples/spark/spark_advanced_options.py defines the helper with no parameters:

def _backend_config():
    """Backend config; uses SPARK_TEST_NAMESPACE in CI."""
    return KubernetesBackendConfig(namespace=os.environ.get("SPARK_TEST_NAMESPACE", "default"))

Four of the five call sites invoke it correctly, but example 5 passes an argument:

line	call
54	_backend_config()
101	_backend_config()
141	_backend_config()
185	_backend_config()
217	_backend_config("spark-production")

Line 217 raises:

TypeError: _backend_config() takes 0 positional arguments but 1 was given

main() wraps every example in a broad except Exception, so the user never
sees the TypeError itself — example 5 silently never runs and the script
prints the misleading advice instead:

Error: _backend_config() takes 0 positional arguments but 1 was given

Note: Make sure you have:
  1. Spark Operator installed with SparkConnect CRD
  2. Proper RBAC permissions configured
  ...

ALL EXAMPLES COMPLETE! is never printed. The in-cluster E2E run is unaffected
because SPARK_E2E_RUN_IN_CLUSTER=1 skips example 5, which is why this has gone
unnoticed in CI.

Fix

Drop the stray argument so line 217 matches the other four call sites.

I deliberately did not make _backend_config accept a namespace: the
namespace must stay environment-driven (SPARK_TEST_NAMESPACE) for the
in-cluster E2E run, and this example already names its session through the
options pattern it is demonstrating:

Name(_e2e_session_name("prod-etl-session")),

Verification

Signature replay against main (3febcd7):

signature: ()
  _backend_config()                    -> OK
  _backend_config("spark-production")  -> TypeError: too many positional arguments
call sites: line 54 (0 args), 101 (0), 141 (0), 185 (0), 217 (1 arg)

After the patch, no call site passes an argument. Diff is one line.

🤖 Generated with Claude Code

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[tariq-hasan]

/ok-to-test
/retest

[tariq-hasan]

Thanks!
/lgtm