test: parallelize sea tests when there's enough disk space

[joyeecheung]

The sea tests are only run sequentially to avoid taking too much disk space. When there is enough disk space, however, it's better to run them in parallel, as these tests tend to be slow.

On a 12 core mackbook with enough disk space

Before

$ tools/test.py sea
[02:10|% 100|+  20|-   0]: Done

After

$ tools/test.py sea
[00:28|% 100|+  20|-   0]: Done

[nodejs-github-bot]

Review requested:

• @nodejs/single-executable

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70068/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.55%. Comparing base (be60e4e) to head (91ce6ed).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #60604   +/-   ##
=======================================
  Coverage   88.55%   88.55%           
=======================================
  Files         704      704           
  Lines      208072   208087   +15     
  Branches    40080    40087    +7     
=======================================
+ Hits       184265   184279   +14     
+ Misses      15832    15826    -6     
- Partials     7975     7982    +7     

see 28 files with indirect coverage changes

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