[cli] Fix updating of gitignore in vercel link

[msimulcik]

Related Issues

Fixes https://github.com/vercel/runtimes/issues/249

📋 Checklist

Tests

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR

[codecov]

Codecov Report

Merging #6986 (84301e9) into main (c3abf73) will decrease coverage by 0.04%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##             main    #6986      +/-   ##
==========================================
- Coverage   51.55%   51.51%   -0.05%     
==========================================
  Files         128      128              
  Lines        4971     4975       +4     
  Branches     1168     1167       -1     
==========================================
  Hits         2563     2563              
- Misses       2402     2406       +4     
  Partials        6        6              

Impacted Files	Coverage Δ
packages/cli/src/util/projects/link.ts	57.60% <46.15%> (-1.91%)	⬇️

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