fix: select musl JDK artifacts on Alpine for five distributions (#1220)

On Alpine, `getPlatformOption()` returned the glibc platform key for
Dragonwell, Corretto, Zulu, Liberica and Liberica NIK, so the action
resolved and installed a glibc JDK that cannot run under musl.

Add a shared `isAlpineLinux()` helper and use it to select each vendor's
musl artifacts:

| distribution | glibc         | musl           |
| ------------ | ------------- | -------------- |
| Dragonwell   | `linux`       | `alpine-linux` |
| Corretto     | `linux`       | `alpine`       |
| Zulu         | `linux_glibc` | `linux_musl`   |
| Liberica     | `linux`       | `linux-musl`   |
| Liberica NIK | `linux`       | `linux-musl`   |

Each key was verified against the vendor's live metadata API or manifest.

There is deliberately no silent fallback to glibc when a vendor has no
musl build for the requested version or architecture: the existing "could
not find a version that satisfies" error fires instead. This matches the
behaviour Temurin and SapMachine already have, and a glibc JDK would not
run on musl anyway.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 74248bb0-72af-41d8-b85d-b0f5836e68db

src/distributions/liberica-nik/installer.ts

@@ -14,6 +14,7 @@ import {
 } from '../../util.js';
 import * as core from '@actions/core';
 import {ArchitectureOptions, NikVersion, OsVersions} from './models.js';
+import {isAlpineLinux} from '../platform-types.js';
 import fs from 'fs';
 import path from 'path';
 
@@ -156,7 +157,7 @@ export class LibericaNikDistributions extends JavaBase {
       case 'cygwin':
         return 'windows';
       case 'linux':
-        return 'linux';
+        return isAlpineLinux(platform) ? 'linux-musl' : 'linux';
       default:
         throw new Error(
           `Platform '${platform}' is not supported. Supported platforms: ${supportedPlatform}`