test: Make the psake/Invoke-Build task drift guard able to fail, in both directions

[tablackburn]

Summary

• Repairs the task drift guard in tests/IBTasks.tests.ps1, which has never compared a task
  name (The psake/Invoke-Build task drift guard compares nothing against nothing #215), and makes the comparison bidirectional
• Three defects cancelled out, so the test passed on any input; all three are fixed together,
  because fixing any one alone turns the test red for the wrong reason
• The other Describe blocks in the file (added in IB.tasks.ps1 reads a nonexistent CodeCoverage.OutputFormat setting, so Invoke-Build users get $null #178 and $PSBPreference.Sign.SkipCertificateValidation has no effect on the Store and Thumbprint sources it is documented for #193) are untouched

The three defects

1. $IBTasksResult was assigned in one It and read in the next. Each It runs in its own
   scope, and the $IBTasksResult = $null at the Describe level runs at discovery only, so
   the reader saw $null. The Invoke-Build job now runs once in the Describe's BeforeAll
   and both It blocks read $script:invokeBuildTaskName.
2. Invoke-PSake -docs writes a formatted table, so format records crossed the job
   boundary, not task objects. They have no Name property, so every psake name was $null.
   Get-PSakeScriptTasks -buildFile returns task objects, and the job projects the names to
   strings before they are serialized.
3. Not in the issue: $IBTasksResult.All is an OrderedDictionary keyed by task name, so
   .All.Name is a lookup for a key called Name, not an enumeration of the names. It is
   empty in-process and after serialization alike, so fixing only the scoping defect would
   still have compared psake's tasks against an empty list. The job returns .All.Keys.

$null -notin $null is False, so the old throw never fired, and the closing
Should -Not -BeNullOrEmpty passed on an array of 21 nulls.

Both directions

A task defined in IB.tasks.ps1 and forgotten in psakeFile.ps1 leaves psake consumers
without it — the same defect as #178 and #193 with the files swapped — and nothing else in the
suite catches it. The It is renamed to defines the same tasks in both task files and
asserts $missingFromInvokeBuild and $missingFromPsake separately, each with its own
-Because, matching the Signing settings referenced by the task files block in this file.

Each runner's own entry point is excluded on its own side, with the reason in a comment: psake
answers to default and ?, Invoke-Build to .. Nothing else is excluded.

Test plan

./build.ps1 -Task Test on Windows 11, PowerShell 7.6.5, Pester 6.1.0, psake 5.0.4,
InvokeBuild 5.14.23. Each run was checked against the rebuilt files in Output/ to confirm the
probe was present or absent as intended.

Red, psake task missing from Invoke-Build — Task Sign SignModule, SignCatalog renamed to
Task RenamedSignTask ... in PowerShellBuild/IB.tasks.ps1:

  [-] defines the same tasks in both task files
   Expected $null or empty, because IB.tasks.ps1 must define every task psakeFile.ps1
   defines, but got 'Sign'.
Tests Passed: 590, Failed: 1, Skipped: 3

Red, Invoke-Build task missing from psake — Task ExtraInvokeBuildTask {} appended to
PowerShellBuild/IB.tasks.ps1. An addition is the only probe that isolates this direction,
since a rename diverges both at once:

  [-] defines the same tasks in both task files
   Expected $null or empty, because psakeFile.ps1 must define every task IB.tasks.ps1
   defines, but got 'ExtraInvokeBuildTask'.
Tests Passed: 590, Failed: 1, Skipped: 3

Before this change, neither divergence failed anything — the measurement in #215.

Green — both probes reverted, neither name present in the built task files:

  [+] IB.tasks.ps1 exists
  [+] Parseable by invoke-build
  [+] defines the same tasks in both task files
Tests Passed: 591, Failed: 0, Skipped: 3

Both runners report the same 16 tasks.

Notes

• Local variable names in the BeforeAll lost their abbreviations ($outputModVerDir became
  $outputModuleVersionPath) while those lines were being edited, per the shorthand
  instructions.
• No CHANGELOG.md entry: a test-suite repair with no change to the shipped module, and
  repository-specific.instructions.md scopes the changelog to user-facing changes.

Closes #215

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Test Results

    4 files  ±0    889 suites  ±0   2m 6s ⏱️ -21s
  596 tests ±0    593 ✅ ±0   3 💤 ±0  0 ❌ ±0 
2 367 runs  ±0  2 295 ✅ ±0  72 💤 ±0  0 ❌ ±0 

Results for commit a28ac72. ± Comparison against base commit 3ea9e82.

This pull request removes 1 and adds 1 tests. Note that renamed tests count towards both.

Invoke-Build Tasks.Contains all the tasks that were in the Psake file

Invoke-Build Tasks.defines the same tasks in both task files

♻️ This comment has been updated with latest results.