Publish-PSBuildModule reports success when the publish fails #203

Publish-PSBuildModule reports success for a module it never published.

What happens

Publish-Module reports a failed publish as a non-terminating error — an
unregistered repository, a rejected API key, a repository the credential cannot
authenticate to. Publish-PSBuildModule calls it at the default
$ErrorActionPreference, so the error is written to the error stream and the
command returns normally. Publish-PSBuildModule then returns normally after
it, and the Publish task in both psakeFile.ps1 and IB.tasks.ps1 reports
success.

Measured against the built module on main:

Publish-PSBuildModule -Path $existingModulePath -Version '1.0.0' `
    -Repository 'PSBuildNoSuchRepository' -NuGetApiKey 'not-a-real-key'
# Get-PackageSource: Unable to find repository 'PSBuildNoSuchRepository'.
# ...and then it returns. Nothing throws.

Why it matters

This is the release path. .github/workflows/publish.yaml runs
./build.ps1 -Task Publish when a GitHub release is published, and a consumer's
release workflow does the same. A green build after a publish that did not
happen is the worst failure mode this particular function has: the artifact is
simply absent from the gallery and nothing said so.

It was invisible until now because Publish-PSBuildModule had no tests at all
(#103) — 0 of 21 instructions covered, literally rather
than as an artifact of background-job instrumentation.

Fix

Default -ErrorAction Stop on the Publish-Module call, forwarded through the
same $PSBoundParameters loop that already forwards NuGetApiKey and
Credential, so an explicit -ErrorAction from the caller still wins.

Fixed alongside the test coverage in #103.