test: fix debug test crashes caused by sea tests

[vmoroz]

When we compile for debug on Windows we have the tests crashing with the error log shown below.
The root cause of the issue is that when the SEA tests are probing for parallel execution they call context.GetVm('none', 'none').
This call results with trying to use Release\node.exe that is not created for debug-only builds.

In this PR we record the first --mode passed to tools\test.py and then we use it as a fallback when the context.GetVm('none', 'none') raises an exception.

Since I do not know the full background why we use none/none and why GetVm unconditionally returns the Release path in that case, this is the best solution that I could come with. Feel free to propose a better version.

This PR and and PR #60806 finally unblock the test runs on Windows while working on the code.

The error log being addressed by this PR:

Node.js v26.0.0-pre
running 'python tools\test.py --mode=debug  js-native-api'
Traceback (most recent call last):
  File "E:\GitHub\nodejs\node\tools\test.py", line 1854, in <module>
    sys.exit(Main())
             ^^^^^^
  File "E:\GitHub\nodejs\node\tools\test.py", line 1707, in Main
    root.GetTestStatus(context, sections, defs)
  File "E:\GitHub\nodejs\node\tools\test.py", line 942, in GetTestStatus
    tests_repos.GetTestStatus(context, sections, defs)
  File "E:\GitHub\nodejs\node\tools\test.py", line 909, in GetTestStatus
    self.GetConfiguration(context).GetTestStatus(sections, defs)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:\GitHub\nodejs\node\tools\test.py", line 891, in GetConfiguration
    self.config = module.GetConfiguration(context, self.path)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:\GitHub\nodejs\node\test\sea\testcfg.py", line 8, in GetConfiguration
    vm = context.GetVm('none', 'none')
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "E:\GitHub\nodejs\node\tools\test.py", line 991, in GetVm
    raise ValueError('Could not find executable. Should be ' + name)
ValueError: Could not find executable. Should be E:\GitHub\nodejs\node\Release\node.exe

[nodejs-github-bot]

Review requested:

• @nodejs/single-executable

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.56%. Comparing base (93c2581) to head (11fa798).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60807      +/-   ##
==========================================
+ Coverage   88.43%   88.56%   +0.12%     
==========================================
  Files         703      703              
  Lines      208235   208254      +19     
  Branches    40085    40176      +91     
==========================================
+ Hits       184162   184430     +268     
+ Misses      16069    15841     -228     
+ Partials     8004     7983      -21     

see 45 files with indirect coverage changes

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