GitHub actions not reporting warnings

[simsong]

See https://github.com/simsong/bulk_extractor/actions/runs/4715021826/jobs/8361732786
Why isn't this warning causing the Action to fail?

In file included from be20_api/scanner_set.cpp:30:
be20_api/machine_stats.h: In static member function ‘static float machine_stats::get_cpu_percentage()’:
be20_api/machine_stats.h:37:14: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   37 |         fgets(buf,sizeof(buf),f);           /* read the first line */
      |         ~~~~~^~~~~~~~~~~~~~~~~~~
be20_api/machine_stats.h:38:14: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   38 |         fgets(buf,sizeof(buf),f);           /* read the second line */
      |         ~~~~~^~~~~~~~~~~~~~~~~~~