Update license-file metadata in pyproject.toml

[PProfizi]

Fix #842

ERROR    InvalidDistribution: Invalid distribution metadata: unrecognized or    
         malformed field 'license-file'              

[PProfizi]

@moe-ad it looks like the fix is not working

Traceback (most recent call last):
  File "C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\pyproject_hooks\_in_process\_in_process.py", line 389, in <module>
    main()
  File "C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\pyproject_hooks\_in_process\_in_process.py", line 373, in main
    json_out["return_val"] = hook(**hook_input["kwargs"])
  File "C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\pyproject_hooks\_in_process\_in_process.py", line 143, in get_requires_for_build_wheel
    return hook(config_settings)
  File "C:\Users\runneradmin\AppData\Local\Temp\build-env-_pzbaobv\lib\site-packages\flit_core\buildapi.py", line 23, in get_requires_for_build_wheel
    info = read_flit_config(pyproj_toml)
  File "C:\Users\runneradmin\AppData\Local\Temp\build-env-_pzbaobv\lib\site-packages\flit_core\config.py", line 85, in read_flit_config
    return prep_toml_config(d, path)
  File "C:\Users\runneradmin\AppData\Local\Temp\build-env-_pzbaobv\lib\site-packages\flit_core\config.py", line 112, in prep_toml_config
    loaded_cfg = read_pep621_metadata(d['project'], path)
  File "C:\Users\runneradmin\AppData\Local\Temp\build-env-_pzbaobv\lib\site-packages\flit_core\config.py", line 667, in read_pep621_metadata
    raise ConfigError(
flit_core.config.ConfigError: License classifiers are deprecated in favor of the license expression. Remove the 'License :: OSI Approved :: MIT License' classifier

ERROR Backend subprocess exited when trying to invoke get_requires_for_build_wheel

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.12%. Comparing base (9f5b534) to head (76d8363).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #845   +/-   ##
=======================================
  Coverage   85.12%   85.12%           
=======================================
  Files          52       52           
  Lines        5210     5210           
=======================================
  Hits         4435     4435           
  Misses        775      775           

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[jorgepiloto]

Thanks for fixing this, @PProfizi.