Added failing test for forward slashed branch name

[taras]

Motivation

backstage/backstage#2815

Approach

I created a failing test for this scenario.

🤷‍♀️ not sure how to fix it. Open to suggestions.

[IonicaBizau]

Well... the pathname could be parsed depending on what you are expecting it to be...

In your example, if I understand well, there are the following cases:

https://github.com/42IonicaBizau/git-url-parse/blob/dependabot/npm_and_yarn/graphql-15.0.0/package.json

Branch: dependabot 
Filepath: npm_and_yarn/graphql-15.0.0/package.json

Branch: dependabot/npm_and_yarn
Filepath: graphql-15.0.0/package.json

Branch: dependabot/npm_and_yarn/graphql-15.0.0
Filepath: package.json

Perhaps even this:
Branch: dependabot/npm_and_yarn/graphql-15.0.0/package.json
No filepath

[taras]

Yeah, this is the tricky bit. There isn't really a way to know where the branch name ends and file path begins.