CI: unblock MySQL 9.7 matrix job by making removed InnoDB option non-fatal

[Copilot]

The test (ubuntu-latest, 1.27, 9.7) Actions job failed before tests started because MySQL 9.7 rejects innodb_log_file_size at startup. This change updates CI MySQL config so newer versions ignore that legacy option instead of aborting initialization.

• Root cause

  • MySQL setup in .github/workflows/test.yml passed innodb_log_file_size=256MB via my-cnf.
  • On MySQL 9.7, that variable is unknown and causes mysqld --initialize-insecure to fail.

• Change

  • Switched to the loose- variant for cross-version compatibility in workflow config:
    • innodb_log_file_size=256MB → loose-innodb_log_file_size=256MB

• Why this is safe across matrix versions

  • Older MySQL versions still apply the option.
  • Versions that removed it ignore it without failing startup.

my-cnf: |
  loose-innodb_log_file_size=256MB
  innodb_buffer_pool_size=512MB
  max_allowed_packet=48MB