docs: refer to "squash" in help screen for git node land

[sxa]

Since this is my first contribution to NCU I'll note that npm run test-all as documented in the contributing guide doesn't seem to be valid. I have run npm test on this though. Based on the fact it looks like the target was removed in #670 I'll submit a follow on PR to remove that step from the guide.

This change is because I was looking for the option on git node land to squash commits when landing nodejs/node#64193 (which I was pretty sure I'd used on the past) but it doesn't have squash in the help screen as it's named fixupAll and this will allow git node land --help | grep squash to find it. I may also add a reference to this as a recommendation in the main node collaborator guide if people thing that's appropriate.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.52%. Comparing base (2d1085f) to head (1dd68d8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1108   +/-   ##
=======================================
  Coverage   64.52%   64.52%           
=======================================
  Files          45       45           
  Lines        7003     7003           
=======================================
  Hits         4519     4519           
  Misses       2484     2484           

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[sxa]

Force push to squash as there was a linter error when I accepted @Renegade334's suggested change related to the Co-authored-by line that was added.