🐞 CI: V7 pipeline: use `mklink` properly
🐞 CI: V7 pipeline: use `mklink` properly

It appears we need to _explicitly_ define the target link name, unlike
the UNIX's `ln`.

fixes <https://ci.cli.fun/teams/main/pipelines/V7/jobs/units/builds/1394>:
```
mklink /D C:\...\cli C:\...\gopath\src\code.cloudfoundry.org\
Cannot create a file when that file already exists.
```

[finishes #167390121]

Co-authored-by: Reid Mitchell <15b84f3bcf1e0a1a99817cc9360cedc980d7c5b6@pivotal.io>
Co-authored-by: Brian Cunnie <c96b911daecac34294af5ecfb5cb3aa7cd7901af@pivotal.io>

cloudfoundry/cli,cloudfoundry/cli,cloudfoundry/cli