fix(testing): strip relative paths (as well as file:// paths) from snapshot test subprocess stderr

[dandv]

Fix #7080.

formatTestError in snapshot_test.ts strips Deno's Check <path> diagnostic lines from subprocess stderr, but the
regex only matched file:// URLs. Deno outputs file:// URLs when the working dir is 3+ levels from the filesystem root, but it outputs relative paths (e.g. ../../tmp/…) when the working directory is fewer than 3 levels from /. That left the line unstripped and caused assertNoError to throw.

This fix broadens the regex from /^Check file:\/\/(.+)\n/gm to /^Check .+\n/gm so it matches any path format Deno emits.

Authored with help from Claude 4.6.

[CLAassistant]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.41%. Comparing base (1cd63ca) to head (83602d8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7081   +/-   ##
=======================================
  Coverage   94.41%   94.41%           
=======================================
  Files         630      630           
  Lines       50490    50490           
  Branches     8949     8949           
=======================================
+ Hits        47669    47670    +1     
  Misses       2249     2249           
+ Partials      572      571    -1     

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