Tezt/rollups: Fix flakiness for RISC-V PVM refutation game tests

Part of RV-566.

What

A small fix for the refutation game integration tests needed for the RISC-V PVM tests. The scenario tests whether a conflict has been detected by the honest rollup operator by waiting on the smart_rollup_node_conflict_detected.v0 event. The callback does not consistently get called in the configuration used for the RISC-V PVM with slower block production.

Why

An otherwise successful test would fail this check.

How

Use the more reliable RPC.get_chain_block_context_smart_rollups_smart_rollup_staker_games as a proxy. If a game for the honest node is ever in progress, a conflict must have been detected first.

Manually Testing

The full refutation game test can be run on the vdum@tezt-felix/rv-698 branch:

dune exec tezt/tests/main.exe -- riscv ci_disabled --verbose

Tasks for the Author

• Link all Linear issues related to this MR using magic words (e.g. part of, relates to, closes).
• Eliminate dead code and other spurious artefacts introduced in your changes.
• Document new public functions, methods and types.
• Make sure the documentation for updated functions, methods, and types is correct.
• Add tests for bugs that have been fixed.
• Put in reasonable effort to ensure that CI will pass.
  • make -C src/riscv
  • dune build src/lib_riscv
  • dune build src/rust_deps
• Benchmark performance and populate the table above if needed.
• Explain changes to regression test captures when applicable.
• Write commit messages to reflect the changes they're about.
• Self-review your changes to ensure they are high-quality.
• Complete all of the above before assigning this MR to reviewers.