Fix root-safe provider test runtime stub [reduced-it]

[binmahone]

Follow-up to #15944 and #15957.

Description

After both Iceberg packaging changes reached main, package-parallel-worlds.py began reading system_runtime_path from the loaded iceberg_runtime.py module. RootSafeProviderSelectionTest creates a minimal fake version of that module, but the fixture still defined only coordinates. As a result, the standard-assembler subtest failed with KeyError: 'system_runtime_path' before Maven compilation, causing install and verify matrix jobs on subsequent pull requests to fail or be canceled by fail-fast.

This change adds the missing system_runtime_path function to the fake module. It returns None, matching the test fixture's existing behavior when no explicit system Iceberg runtime is configured. Production code is unchanged.

Validation on current main (b23ab02e986767dfd26fde2e221d58658d9a2179):

$ python3 dist/scripts/tests/test_root_safe_provider_selection.py
.
----------------------------------------------------------------------
Ran 1 test in 0.251s

OK

The failure was also reproduced before the fixture change with the same KeyError reported by the Maven matrix in #15982.

This change was prepared with AI assistance and reviewed by the author.

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge and correctly restores the test fixture’s compatibility with the assembler.

Summary

• Adds the missing fake runtime-module interface.
• Preserves the fixture’s intended no-system-runtime configuration.
• Changes test code only; production packaging behavior is unchanged.

_{Reviews (1) · Last reviewed commit: "Fix root-safe provider test runtime stub"}

[gerashegalov]

LGTM

[gerashegalov]

I was including it in #15958. But a dedicated fix is faster.

[gerashegalov]

build