Fix CI: update whir to fix batch_size assertion on Linux aarch64

[Bisht13]

Summary

• Update whir rev to include fix for batch_size underflow in matrix_commit::hash_rows_serial (Fix batch_size underflow in matrix_commit for small cache sizes WizardOfMenlo/whir#229)
• Add RUST_BACKTRACE=1 to CI env for future debuggability

Root Cause

small_sha and complete_age_check tests panic on CI (ubuntu-24.04-arm, Linux aarch64) with:

assertion failed: batch_size >= 1
at whir/src/protocols/matrix_commit.rs:355

On Linux aarch64, workload_size falls through to the 32KB default. With starting_log_inv_rate = 2 (4x codeword expansion), message_size exceeds target = 4096, making target / message_size = 0 → batch_size = 0.

The whir fix (1) adds .max(1) before next_multiple_of and (2) assigns Linux aarch64 a 64KB cache size matching Graviton/Ampere L1d.