Use File in Cli.Args

[fthomas]

This uses File in Cli.Args so that we don't need Sync when converting
from Args to Config.

[codecov]

Codecov Report

Merging #1653 into master will increase coverage by 0.08%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master    #1653      +/-   ##
==========================================
+ Coverage   71.68%   71.76%   +0.08%     
==========================================
  Files         114      114              
  Lines        1875     1877       +2     
  Branches       57       55       -2     
==========================================
+ Hits         1344     1347       +3     
+ Misses        531      530       -1     

Impacted Files	Coverage Δ
...ala/org/scalasteward/core/application/Config.scala	0.00% <0.00%> (ø)
...la/org/scalasteward/core/application/Context.scala	0.00% <0.00%> (ø)
.../scala/org/scalasteward/core/application/Cli.scala	100.00% <100.00%> (ø)

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