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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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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