expect not properly spawning Stockfish in github actions.

[vondele]

CI actually doesn't run correctly, i.e. in the actions some tests are effectively not run. It is specific to running it in the actions the same test locally seems to work. In CI we have this debug output:

 spawn ./stockfish
parent: waiting for sync byte
parent: telling child to go ahead
parent: now unsynchronized from child
spawn: returns {3784}

expect: does "" (spawn_id exp3) match glob pattern "Stockfish"? no
expect: read eof
expect: set expect_out(spawn_id) "exp0"
expect: set expect_out(buffer) ""
instrumented testing failed on line 296

compared to locally:

spawn ./stockfish
parent: waiting for sync byte
parent: telling child to go ahead
parent: now unsynchronized from child
spawn: returns {16146}

expect: does "" (spawn_id exp4) match glob pattern "Stockfish"? no
Stockfish dev-20240413-c55ae376 by the Stockfish developers (see AUTHORS file)
expect: does "Stockfish dev-20240413-c55ae376 by the Stockfish developers (see AUTHORS file)\r\n" (spawn_id exp4) match glob pattern "Stockfish"? yes
expect: set expect_out(0,string) "Stockfish"
expect: set expect_out(spawn_id) "exp4"
expect: set expect_out(buffer) "Stockfish"
send: sending "uci\n" to { exp4 }
...

My interpretation of this is that in CI expect spawns stockfish but it (or whatever pipe that connects expect to stockfish) closes on startup, leading to eof. While locally there is no issue. An additional tests shows that expect can spawn things (e.g. using cat instead of stockfish works) also in CI.

Originally posted by @vondele in #5181 (comment)