ci: unpin Node.js, test against lts/* and latest

[tomas-zijdemans]

Unpins the Node CI matrix from 24.2.0 and runs the tests against lts/* and latest instead.

The pin was a workaround for nodejs/node#58826, an fs.chown crash on uid -1 that @kt3k hit on Node 24.3. The fix shipped in Node 24.4.0 on July 9, 2025, so the TODO to restore latest has been actionable for a year.

Why two entries: latest is Node 26, which ships V8 14 builtins like Uint8Array.prototype.toBase64. Node 24 LTS does not have them, and it is what most @std consumers on npm run until 2028. Keeping lts/* in the matrix means a change that leans on a 26-only builtin fails CI instead of failing users.

Tested by CI itself. The test-node job now runs twice, once per Node line.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.00%. Comparing base (ad7c87b) to head (9644bc0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7241   +/-   ##
=======================================
  Coverage   95.00%   95.00%           
=======================================
  Files         617      618    +1     
  Lines       51674    51677    +3     
  Branches     9326     9326           
=======================================
+ Hits        49093    49097    +4     
  Misses       2038     2038           
+ Partials      543      542    -1     

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