Fix dart fix command line arg

[fzyzcjy]

/cc @AlexV525

Otherwise it error like:

6.8s] Parse ⠂
[2024-09-11T12:20:37.601Z WARN frb_codegen/src/library/commands/command_runner.rs:153] command=cd "/Volumes/MyExternal/ExternalRefCode/flutter_rust_bridge/frb_example/dart_minimal" && "sh" "-c" "\"dart\" \"fix\" \"--apply\" \"lib/src/rust/api/minimal.dart\" \"lib/src/rust/frb_generated.io.dart\" \"lib/src/rust/frb_generated.web.dart\" \"lib/src/rust/frb_generated.dart\"" stdout= stderr=Only one file or directory is expected.

Usage: dart fix [arguments]
-h, --help                      Print this usage information.
-n, --dry-run                   Preview the proposed changes but make no changes.
    --apply                     Apply the proposed changes.
    --code=<code1,code2,...>    Apply fixes for one (or more) diagnostic codes.

Run "dart help" to see global options.

[2024-09-11T12:20:37.601Z WARN frb_codegen/src/library/codegen/polisher/mod.rs:93] Fail to execute_dart_fix, but continue to run.
Error details: Err(Command execution failed: Only one file or directory is expected.

Usage: dart fix [arguments]
-h, --help                      Print this usage information.
-n, --dry-run                   Preview the proposed changes but make no changes.
    --apply                     Apply the proposed changes.
    --code=<code1,code2,...>    Apply fixes for one (or more) diagnostic codes.

Run "dart help" to see global options.
)
[12.6s] Parse  
  └── [12.6s] Cargo expand & syn parse  
  └── [0.0s] Parse HIR  
  └── [0.0s] Parse MIR  
[0.0s] Generate  
[1.4s] Polish  
  └── [0.2s] Run Dart fix  
  └── [1.1s] Run Dart formatter  
  └── [0.1s] Run Rust formatter                                                                                          Done!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.97%. Comparing base (870e5fc) to head (8e613e8).
Report is 15 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2288   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files         490      490           
  Lines       20286    20276   -10     
=======================================
- Hits        20078    20069    -9     
+ Misses        208      207    -1     

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