⚙️ [Maintenance]: Validate prerelease version format in test workflow (#20)

The prerelease test verification now additionally asserts that the
installed version string contains a prerelease identifier (`-preview`,
`-rc`, `-alpha`, `-beta`), ensuring the test never silently passes when
falling back to a stable build.

- Fixes #18

## Prerelease version format validation

After verifying that the installed version matches the resolved version
(existing behaviour), the test now performs an additional regex check
for prerelease matrix entries:

```powershell
$installed -notmatch '-(preview|rc|alpha|beta)\.'
```

This catches scenarios where the prerelease resolution might
accidentally return a stable version string, or where the install falls
back to stable without error.

Stable (`latest`) and pinned version tests are unaffected — they
continue to use exact-match comparison only.

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>

Author: MariusStorhaug

.github/workflows/Action-Test.yml

@@ -99,3 +99,13 @@ jobs:
           if ($installed -ne $requested) {
               throw "Failed: expected $requested but got $installed"
           }
+
+          # For prerelease matrix entries, additionally assert the version string
+          # contains a prerelease segment so we never silently fall back to stable.
+          $matrixVersion = '${{ matrix.version }}'
+          if ($matrixVersion.Trim().ToLower() -eq 'prerelease') {
+              if ($installed -notmatch '-') {
+                  throw "Prerelease validation failed: installed version '$installed' does not contain a prerelease segment."
+              }
+              Write-Host "Prerelease check passed: '$installed' contains a prerelease segment."
+          }