refactor(testing): add instructions to update snapshots

[WWRS]

closes #6542

I chose to use [TEST FILE PATH] instead of adding the file path so that the tests in snapshot_test.ts.snap wouldn't be affected by where the test is being run from. It would probably be possible to add the relative path using something like

PlatformPath.relative(Deno.cwd(), context.origin)

though this would require additional testing

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.08%. Comparing base (616f66d) to head (593dee8).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6543   +/-   ##
=======================================
  Coverage   95.08%   95.08%           
=======================================
  Files         576      576           
  Lines       43345    43346    +1     
  Branches     6466     6466           
=======================================
+ Hits        41216    41217    +1     
  Misses       2089     2089           
  Partials       40       40           

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[kt3k]

I chose to use [TEST FILE PATH] instead of adding the file path so that the tests in snapshot_test.ts.snap wouldn't be affected by where the test is being run from.

That sounds good. I also updated the placeholder to [files]... to align it to deno test --help output

[kt3k]

LGTM. Nice! Thanks