Cargo.toml: set "default-features = false" for onig

[cakebaker]

This PR sets default-features = false for onig in Cargo.toml. Without this setting, I get the following error when trying to run cargo run --bin find find --help:

error: failed to run custom build command for `onig_sys v69.8.1`

Caused by:
  process didn't exit successfully: `/home/dho/projects/findutils/target/debug/build/onig_sys-0c27472ef7fa82d9/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-env-changed=RUSTONIG_DYNAMIC_LIBONIG
  cargo:rerun-if-env-changed=RUSTONIG_STATIC_LIBONIG
  cargo:rerun-if-env-changed=RUSTONIG_SYSTEM_LIBONIG

  --- stderr
  thread 'main' panicked at /home/dho/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.60/src/fallback.rs:791:9:
  "OnigValue_struct_(unnamed_at_oniguruma/src/oniguruma_h_786_3)" is not a valid Ident
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (ae6143f) 59.37% compared to head (faf7358) 57.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #313 +/- ## ========================================== - Coverage 59.37% 57.00% -2.37% ========================================== Files 30 30 Lines 3655 3652 -3 Branches 872 873 +1 ========================================== - Hits 2170 2082 -88 - Misses 1173 1267 +94 + Partials 312 303 -9 ```

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