Do not test benchmarks in CI

[BD103]

Our CI tool currently runs cargo test --benches:

bevy/tools/ci/src/commands/test.rs

Line 20 in 00722b8

"cargo test --workspace --lib --bins --tests --benches {no_fail_fast}"

Because our benchmarks use a custom harness, though, they do not detect this and just run all benchmarks. This is undesired because benchmarks are lengthy and resource-intensive, and should not contain unit tests. The --benches flag should be removed.