Add Repo.toPath

[fthomas]

This adds Repo.toPath which has currently the same implementation as
Repo.show. show is used as representation in log messages while
toPath is used as path components.

This allows us in #2281 to use owner/repo:branch for show and
owner/repo/branch for toPath.

[codecov]

Codecov Report

Merging #2292 (425b3f0) into master (13104a9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2292   +/-   ##
=======================================
  Coverage   77.86%   77.86%           
=======================================
  Files         135      135           
  Lines        2286     2286           
  Branches       58       59    +1     
=======================================
  Hits         1780     1780           
  Misses        506      506           

Impacted Files	Coverage Δ
...main/scala/org/scalasteward/core/vcs/package.scala	100.00% <ø> (ø)
...in/scala/org/scalasteward/core/vcs/data/Repo.scala	100.00% <100.00%> (ø)

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